WRC mainclass from 2027

[saco0o]

i have this especific doubt on the R5s:
if i had the money to just install the roll cage safety cell specs on an Audi S1 or a Renault Megane, have the engine on the rules specs... can i simply enter and compete in wrc2/erc? or its not allowed? does manufacturers need to authorize this kind of thing? do they need do pay? is something related to homologation? cuz theres lots of models doing tcr and ap4 and none are actual factory teams. why that doesnt happens in rally2?