Can I convert my C501/551 rating into an C500/550/560 or the other way around?

Yes. Airwork Operations has obtained approval to provide up to 100% course credit if you hold a valid rating in the other category. This means:

1. if you hold a C501/551 MP ops rating we can credit 100% of the course towards the C500/550/560 type rating and
   
   
2. if you hold a C500/550/560 rating, we can credit 100% of the course towards the C501/551 MP ops rating.

The same applies correspondingly to instructor certificates (TRI).

The details get a little more messy as we have to differentiate between SP and MP ops on the single pilot side and between PIC and COP on the multi pilot end. But it's possible and we have done dozens of conversions so far with many different NAAs without a hitch.
In order to be eligible for the full credit, your existing rating has to be valid. That's important! Please contact HT Jan Brill to discuss such a credit if desired.