Stand Pose tool
As the name suggests, this will lock any ragdoll into its standing "default" pose, which you can then work on from there. A very useful tool to have.
Easy Bodygroup Tool Easy Bonemerge Tool
Makes some of Gmod's more obnoxious applications easier.
Collision Resizer (Prop Resizer) Ragdoll Resizer
These are probably the addons you are looking for. These are basically mandatory for any vore-related art, especially if you're doing giant/tiny stuff which is basically all vore art.