Just a short feedback:
It took quite a time, but thanks to the great upgrading manual I managed to switch from 9.8.2 to 9.9.0.
I did a lot of customization, so it was very helpful to use some software tool to compare the 9.9.0 files with my customized old files (I used the freeware Diffmerge:
SourceGear | DiffMerge available for linux, mac and win).