Open the package, and use install. The following lines are copied out of the messagewindows. I think the line Warning: Recompiling MRVInet, checksum changed for LCLIntf says why it tries to recompile.
....
Messages, Warnings: 1
Warning: other unit files search path (aka unit path) of "RVMediaLaz 1.0" contains "/home/andi/data/RVMediaTrialLazarusLinux/Source", which belongs to package "RVMediaLaz_Dsgn"
Compile package RVMediaLaz 1.0: Exit code 1, Errors: 1, Warnings: 1
Warning: Recompiling MRVInet, checksum changed for LCLIntf
rvmedialaz.pas(11,3) Fatal: Cannot find MRVInet used by RVMediaLaz, incompatible ppu=/home/andi/data/RVMediaTrialLazarusLinux/Source/lib/x86_64-linux/MRVInet.ppu, package RVMediaLaz
Well, yes.
Any unit, that is used by your ppu, must be kept unchanged.
If unit A uses unit B, and unit B changes, then unit A must be recompiled. The ppu is no longer valid. That has nothing todo with how the path are set
https://forum.lazarus.freepascal.org/index.php/topic,47582.msg341809.html#msg341809You need the exact version of Lazarus against which RVMediaLaz was compiled. If you use the installer, then it comes with all pre-build ppu (exactly so that 3rd party packages can be installed).
In theory, you should be able to re-build the lazarus packages, and they should end up with the same checksums.
But I do not know the exact details on how fpc computes them.
I would guess that changing optimization level, if it for example changes inline-ability, could change the checksum. I also am not sure, which checksums must match interface, or also implementation....
Also note: checksums are passed up recursively: A uses B uses C => C changes, then B will recompile, and even if B sources did not change, the checksum for B will (as it includes the checksum of all used packages). And the same A changes, as B then has changed.
So if you have ppu only packages there is no touching any of the used packages. No minor fixes, nothing. (This may even mean: no CLEAN rebuild of the IDE, not sure I would think checksums should be the same afterward, but.....)