Hmm, Ok. So I was actually right? Mystery solved then.
@M4j0r probably was trying to say the same thing in a different way?
"Setini" modifying the "initial/default" table that is stored in the EEPROM and is loaded everytime at the beginning (initially).
"Set" modifying only for the current session, on the fly (the table that is already loaded into volatile RAM).
Because the fan spinup at the first seconds has nothing to do. This probably is just something for reliability on all kinds of devices and fans. In general in order for a fan to begin spinning from a stationary position, it needs more power than to simply remain spinning at a lower speed.
So they normally give the fan a powerful spin first, to make sure it doesn't stay jammed.
With that mystery solved I'm ready now to modify the fan curves manually.
Setini is really the important one and the only one you need to edit. The changes will take effect not on the fly, but after power off and on as expected.
I already tested this on a funny board I have.
Still would have been nice a 1 operation solution
Cheers
Yes you was right, the dangerous ones are the "setini" subcommands variants that writes in EEPROM
Btw, additionaly to the 5 commands i mentioned (fanconpolicy, fantbl, hyst, trp, and tshutdown) probably there are others that writes individual settings in the thermal config area too, is just nobody documented them or found, if you want to search a bit remember you can use the subcommand "help" in combination with any other command, this is going to display some help messages in screen about how to use the command, also keep in mind maybe some commands doesnt have any help texts (but they could acept subcommands like "setini" etc...)
For reference... check in the graphs i made, it contains some (i guess partially) official codenames from a code structure published by m4j0r time ago, and the names that matches with the command name
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fanconpolicy changes the value named "policy" (in dark pink) for the fantable of every thermal sensor (CELL/RSX/other)
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fantbl allows to change "TempD", "TempU", and "Duty" of every fan step
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trp changes the value named "ini_trp_cell" or "ini_trp_rsx" (or the other)
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hyst changes the value named "ini_hyst_cell" or "ini_hyst_rsx" (or the other)
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tshutdown changes the value named "shutdown_temp_cell" or "shutdown_temp_rsx" (or the other)
In this list im missing some more to change the "minduty", "maxduty", "select" (this is the one that indicates if is loaded from ROM or RAM, still a bit unknown), "active"
And "thermal_shutdown_time", "initial_fan_duty", "initial_fan_time"... and 3 unkowns
Are a few, but thats all, im guessing there are commands to change most of that values (or all them)
Remember to make a copy of the original thermal config area before changing anything, i dont think that is much risky because incase of corruption in the thermal config area of the EEPROM, at the next reset you are going to power the PS3 in standby (only) so the fan is stopped, this means syscon is not really doing any "logic" with the values for the fantable... in other words it doesnt really matters if the thermal config area is corrupted because syscon is not using it yet when the PS3 is in standby
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That idea of giving the fan an initial "boost" just as a safety meassure to prevent it being stucked with lower speeds worths to be considered, i always thought that boost is because the processors have an instant notable increment of temperature inmediatly when you boot them (is like a violent temperature change, but relative to the ambient temperature)
What i mentioned in my previous post is something i just imagined when i was writing that post... lets say... maybe what happens is that syscon needs some time to complete all his boot sequence, and along that time is not able to "monitor" the thermal sensors and compare the values of the sensors with the tables in the thermal config to find the fan speed following some "logic"
maybe the "brain" of the syscon is busy in that initial times (checking info from CELL, RSX, etc...) so the fan is working in "stupid mode" for 2 seconds

We could try to change the value of "initial_fan_time" to zero and see what happens, but meh, doesnt matters much, i admit i hated it since years ago, but now i realized that is a "feature" implemented in the syscon firmware on purpose and i tend to think that is there for some good reason
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For me, right now is clear that the best way to do this is automated with a program/script because typing the commands several times sucks. There is too much room for human errors by repating things consecutivelly, is easy to lost the concentration because is boring
The "r" command doesnt have that restriction of chunks of 0x40 bytes in mullion syscons but sherwoods have it, and i believe
@M4j0r when he says that using the "EEP" command is more relliable
So... oki, incase of doing this with some assistance (script or program) is easyer to do it with the EEP command
Next thing that would be a great feature (for writing purposes) would be if that program is able to do a comparison of the entire thermal config area in syscon EEPROM (0x200 bytes) with the file we are going to write (another 0x200 bytes) and write only the bytes that differs
The point is... for us is a lot more convenient to share that "thermal config" settings as a single file... but there are lot of bytes filled with 0xFF, and the file we want to write have that same bytes filled with 0xFF too
Overwriting a byte with the same value is pointless, it would be awesome if the program minimizes the writes operations to syscon EEPROM
Lets say... you make a dump of the complete thermal config (0x200 bytes), then you change only 3 bytes located at different offsets , and then you ask to the program to write it entirelly (0x200 bytes) but the program is smarter than us and realizes that only is needed to use the command EEP 3 times with a length of 1 byte each (3 bytes written in total, at different offsets)