dash plastic; can it be fixed?

Who knows what about the "repairability" of dash or console or inner rear quarter plastic?
also rear spoiler? This stuff is "plastic" not fiberglass; so I have my doubts of fiberglass resin taking hold. is there a "plastic" resin, similar to fiberglass that I could work in conjunction with fiberglass cloth?
I'm looking to bridge cracks from the underside, where it would not be seen as installed; re form ugly speaker holes so that different sized speakers, maybe "aim" them while I was at it; and put mold some auxiliary gauge pods into this plastic; also as I am wanting to put a 5 speed in the car with a factory F body console so I may have some mods to do pertaining to that as well.
so who knows what about repairing/modifying this plastic? Lost cause? Damaged parts, basically "scrap"?
Author: volaredon