If i am rebarreling and my current twist rate is 1-14" and i want to go to say a 1-8" to stabelize longer/heavier bullets, Would shorter/lighter bullets still shoot ok in it? Is it a slow twist rate will not stabelize longer bullets but a faster twist rate will still stabelize shorter bullets?

The longer the bullet, the faster the twist needs to be. Depending on the lighter bullet you choose it should shoot OK. Some of the lighter jacketed bullets may come apart twisting them too fast.

And you can't use the standard reloading data as your pressures will rise a bit due to trying to get that light weight bullet up to full rpm.

Take a .223 Rem with a 1-7 twist and try to shot off the shelf 55grain loads. Bullet barrel and velocity don't mix on that one. It'll shot one hole groups with 62 gr and 69 gr bullets