If you want to alter parts, try Apoxy Scuplt. Way better than anything else on the market IMO. I basically carve down a part with an X-acto and then sculpt over it.
What are you using for casting molds and resin? I use Alluminite but I'm looking for something better. The Alluminite casting mold material is good, but the resin I'm using (not sure what number it is but it hardens like a roller blade wheel which is how their website describes it) works well as long as you pour it right away, if you take too long to pour, it thickens and winds up too thick to seep into the details of your mold.
Yup,I switched to loctite crazy glue from model masters pin point when I started doing these figures. I'm going to start casting parts for myself soon. Hopefully I can get Vortious to share some insight on limbs..I find the resin is even easier to work then standard joe plastic..if they where harder,and sanded better I could alter those parts way easier.
I started out doing scale models too. I find that krazy glue works really well on the softer plastic parts. It melts the plastic very well in case you were looking for a good glue to use.