I think the answer to this is yes: Once I complete a character model, I no longer have to recreate that character for other positions correct? Say I make a character standing up…no I want them sitting down. There are tools for manipulating this right?
Yes. This is called “rigging”. There are multiple ways to rig a model, with characters it’s usually done using Armatures (skeletons). Constructing a good armature is not an easy task, but luckily we have an addon for generating a rig for a biped character, called Rigify.
You can see an example of rigging using that addon in this video.