No anykind of problem to change from mineral oil to synthetic....

If the engine was run with mineral oil for years (or maybe from the beginning) switching from mineral oil to synthetic should be done only after the engine is flushed or rebuilt as synthetic oil will loosen all the sludge that built up in the engine over time and all that will run through your engine again.
If you have a rebuild engine you can run mineral oil for the break in period and then switch to synthetic, but I wouldn`t do this after years of using mineral oil unless I know the engine is clean inside. (my personal opinion)

G.

no, both oils are compatible (years ago that may have been different), nothing will happen there.

There are also "washing minerals" in oils, so no need to worry about old mineral oil inside engine. Some oils are more "washing", than others... I have changed from mineral to synthetic without any oil problems. Same with my Ducati friends.... More important is to use very high quality oil and change filter every time and i drive MAXIMUN 5000kms with one set. And i drive normally "long runs" with my bikes, never short distances....