It’s entirely possible to do full repaints and adjust metal properties for every part of the plane.
How to edit the existing liveries colors was explained here already, and you can make those colored parts metallic as well by modifying LIV1_COMP.PNG.dds …
But tp do complete repaints and ignore the current “livery” layout, you first have to make that 4-color livery texture (LIV1_ALB.PNG.dds) transparent.
(This will make the plane completely white)
Then you “just” have to edit the ALMVEO_EXT1_ALB.PNG.DDS(fuselage) and ALMVEO_EXT2_ALB.PNG.DDS(wings) textures and their accompanying COMP files for the metal/roughness properties.
The PA44 Seminole from Carenado is exactly the same in this aspect, and I’ve done a complete repaint livery editing textures only to a drag/drop livery here:
And as a proof of concept, here’s my work in progress Mooney livery, complete repaint (just started):
