Add bar line above fingering number for strings

Anything is possible, but it's not easy. If you can live with a ^ symbol above the fingering then that is available via the Master Palette. Otherwise you will need to get creative and combine symbols or save your own as graphics.

I'd start editing the fingering, position the cursor BEFORE the finger number, press ENTER, press SHIFT+F2. I new dialog "Special character" would appear with three tabs. I'd search for appropriate characters, especially on the first two tabs (the second tab, "Musical symbols" has a lot of symbols). For example, on the first tab on the row above the last one, there are two characters: "-" and "—". The "v" and the rotated square bracket can be found on the second tab. I'd then press the symbol to insert it and close the dialog. Then I'd select just the inserted character (excluding the finger number below it) and using the Properties panel, I'd adjust its font size, boldness, etc. to something that looks good. Finally, in the Properties panel again, I'd adjust the Line spacing until the distance between the inserted character and the finger number below it looks good.