Daan,
yes, I successfully converted from v7 sp2 to v9. it took some work; and frankly I'm not sure I can recreate all the steps. I had Mariadb installed and had successfully gotten v7 sp2 to work; however, I found issues. for example, I could not create user fields without getting a permission error. as I'm not a DBA, I decided I didn't want to mess with SQL issues on permission grants. basically, I'm thinking the Cerious SQL script that created the db had some things missing. so back to MySQL. you will remember that I had serious issues with MySQL not allowing me to set sql_mode = "ansi_quotes". well, I finally managed to get around it after literally months of messing with it. I ended up creating a new windows user profile, completely uninstalling MySQL, then reinstalling it. after that, I used the v7 SQL script on the cerious website. it has issues. as an example, the script on the cerious site has the following commands which are depracated and no longer work, so I had to remove them.
TYPE=InnoDB;
also, to even run the script, I had to use workbench to manually set the "sql mode" to ansi quotes. once I did this, I ran the modified script. it successfully created the v7 sp2 database. next I had to make sure I had 32bit ODBC installed, as TP will apparently not work with 64 bit ODBC. got my ODBC connector created, opened TP v7 sp2, and voila. working database. finally, I restored my actual data / db from backup.
the conversion to v9 at this point was somewhat trivial. I backed up my v7 db again from my now working version. I did this from within the program and also used workbench. I installed v9, and simply used the database / advanced / convert client/server command. it converted the v7 db in place.
finally - I modified my "my.ini" file so that it had sql mode = "ansi_quotes" whenever the mysql service starts. from now on, I'm thinking I'll never have the problem again of being in the wrong mode.
hope this helps. I probably could have given a more logical step wise procedure of what I did; but this should be pretty close.
David