Overall I want to get the usual weights of gold and other materials back into the game, however even if I take it off gold still weights 9 per unit for example so it seems that it doesn't work.

So... is there any way to make it work? perhaps even manually change weights?

Which game? (ERAS, GOF 1.2, GOF 2.0, GOF 2.5?).  Also, I just tried changing the option in each one of those games I listed in an existing saved-game and the weights of all materials on my ship changed.  Procedure was Options, Mod Options, click Realistic Weights option, click Accept, click OK.  When checking F2, Ship screen, everything in the ship's cargo changed weight.  So where are you not seeing the weight change?