That error is triggered by MySQL, not Chevereto. Chevereto only connect to the database and perform queries, anything else depends in your MySQL server.
You should try to check the permissions at your mysql server because since 3.5.3 the system needs permissions to create procedures. The mysql user should have all privileges on the target database to work properly.
Ok, thanks Rodolfo. I contacted my provider to fix that.
But in the meantime, what should I do:
Import my backup of 3.5.2, and bring back all the old files,
or may I stay with 3.5.3 files but without running /install ?
I think that you won't have issues. The new procedures are there to avoid run twice the modify and add statements. But anyway, try to run the thing with all permissions asap and run /install.