I know that there's a default off widget that allows you to move move orders around like supcom. I don't think that you can move building commands though, and when I was using it it felt a little off and hackish. I don't think it worked on buildings.
You can cancel orders by re-issueing the same order.(move commands, fight commands, build commands.) But if a building has started, you cannot easily un-queue that building, because the engine will not accept a build command where a nanoframe has already been placed. If I want a coffee to not build an llt somewhere and just continue on a long mexing run, but it had already started the llt, I will often just take the 10 seconds to re-do the whole quewe to leave that llt at 10%. I'm is different for a couple to build a building and repair a nanoframe.