Sorry for never getting back to this project, but to answer your question yes, if it compiles without error it is safe to upload to the controller. It won’t cause any irreversible damage. Please do monitor it for a few days to make sure nothing pops up. For peace of mind if I ever had an error it would manifest itself immediately, with conditions like not booting, crashing immediately when trying to modify a program, or simply displaying nonsense in the LCD.
The ui.veuphoria.com will only work properly with 2.1.5-6 and the ET FW. Anything else will have changes that will not work at all. I would suggest against using it for anything other than the ET FW.