Every character and every profession. I believe RM2 level bonuses equaled 15, so you could do the same with those (and we did).
Some of those level bonuses apply to entire catagory groups, such as ALL weapons, or ALL athletic, or ALL awareness, or ALL scientific, etc. Those are the ones that need to be closely watched. Most professions that have a bonus that applies to the entire group only have that ONE group. It has been a while since I did the analysis, but I believe there are a couple of professions with two group catagory profession bonuses, but none with +20 to both, which is VERY strong indeed.
So flexible, yes, and I recommend it. Many times players only wish minor adjustments (-5 from lores and adding +5 t0 directed spell for example), and new players don't tend to change anything, but I have seen attempts at abuse (+20 weapopn group, +20 spell group, +10 directed spell was one I said NO to).
Eyes open and all that.