If I file a provisional patent application in the US and then convert it to a full patent in 1 year, can I name additional inventors on that full patent application?
When you say "...and then convert it to a full patent in 1 year..." I assume you mean you would like to file a non-provisional application and claim the benefit of (domestic) priority under 35 U.S.C. 119(e) to the prior-filed provisional application.
The answer is yes, you can add inventor(s) to the non-provisional application. The provisional and non-provisional need only have one inventor in common. See MPEP 211.01(a) which states:
...each prior-filed provisional application must have the same inventor or at least one joint inventor in common with the later-filed application...