You are explicitly allowed to in Star Wars Saga Edition (SWSE), and the rules were balanced around that assumption.
This is less clear in D&D, but offhand, I can't think of any problems that could arise from trading a standard action for a swift action. Allowing the trade of a move action for a swift action would probably be a bad idea, though.
This has been discussed before. It's not technically allowed, but does not seem to break anything - so long as you only use a standard action, and do not allow move actions top take a swift action also.