from what i know if you cut the end of the vine off that vine will not grow out anymore. it will put out secondary vines. for growing on a trellis yes you can. but if you get a big pumpkin growing up there you are going to support it. like a sling or a hammick.

Yes you can.
Depending on how big of a pumpkin you are trying to grow makes some difference because the vine roots and absorbs water and nutrients.
For a Jack-O-Lantern pumpkin you should have no problem hanging the vines.
Or when the vines reach a point where you don't want them to be cut the end off and bury the end of the vine to keep bugs out and see what happens.

Buy what I posted above I would put the excess vines up but have your pumpkins grow on the ground.
Pinch off new pumpkins that are in the air.

I have had a vine go up a tree and it had pumpkins hanging from the tree branches.