Edit: nm, found it
if anyone is interested, i figured how default components are determined by windows setup. sysoc.inf contains a list of all optional components. and each .inf it mentions has the subcomponents.
In the subcomponents look for a line that says Modes=0,1,2,3
this means installed in all install scenarios (clean, upg9x, upgNT, upg2K)
removing the line should no longer make it a default component. (it is explained in commented lines in fxsocm.inf)
i believe modes=0,1,2,3 means
0 is default in clean install, 1 is in Win9x upgrade, 2 is in WINNTupgrade, 3 is in WIN2Kupgrade.. to undefault the component the line should be commented (;) or deleted.