ahhhhh i understand ... mostly u find these params in context of windows ... so probably setting them on linux is really useless.
Not the case - read what I said more closely: If you're on Linux and using the fglrx driver, they do indeed have an effect. Only on AMDGPU (which MUST be used for RX cards) ignores them entirely, IIRC.
oh ... im using "old" HD7990
so on the R-OS Image they would effect mining? and also it should be possible to set temps and fans with claymore than? (not that i would need it but just for understanding)
and on the RX-OS everything is not happening at all?
When i understood it, i would take it on my FAQ section

cause this undervolt/overclock/fansetting stuff is really a FAQ

Yes - I don't use smOS, but his R-OS image pretty much certainly runs fglrx, while the "RX-OS" image would run AMDGPU. Since fglrx still has the ADL interface (which is common to Windows (all) and Linux (fglrx-only)), I believe Claymore's clocking & fanspeed options should function as advertised, yes - the voltage ones, I *highly* doubt it.
Also, what's with the seperate images? Just... dynamically select driver @ boot...
single image smOS for R and RX would nice.