Because Nifskope is something I hate more than anything on this earthy. Really.

When you make a creature (at least in FO3) there is a tab somewhere in teh creature window in the geck, that has a setting called something like 'creatures default scale' and you can set a percentage. If you want the creature twice as big, set it to 200% and all instances of it are 200% the size that nifskope tells them to be. I hope this is what your looking for. (and that it works in NV)

Note that the above suggestion will change all instances of the creature in the game. You can easily scale any reference (be they creatures, containers, doors, lights etc) by holding 's' and dragging the mouse. You can enter a specific number by double-clicking the reference and changing its 'scale' value.

Perfect, thanks a bunch!

In general, you probably don't want to go more then +/- 10% (which is my rule of thumb for static models). Martigen probably has even better ideas of what the limits of scaling are for actors as his mod in FO:3 did dynamic scaling. I think he ran into issues with the size scaling if it was too much.

True but you cant scale something like a leveled monster. So yea, you want to make it its own form first. Also it depends on where your using it for how large or small you want to limit yourself. It has been found roughly 10-15% bigger is the limit as if they are larger than that (for a normal human NPC) they cant walk through doors anymore.