Hi Andrej,
As far as I know doing this is in no way supported and will mean that CA support will basically not touch a system that has this implemented.
If you do it this way and have any issues that you need to raise (no matter what it is, IM only or prov related) you should first copy back the original binary and use this until whatever the issue is is resolved.
If you need more chars, use customfields
Cheers, Atle