Can I change employers in Bulgaria while on an ICT permit?

The ICT permit is purpose-bound. Your employment is restricted to the receiving enterprise or the group of enterprises covered by the transfer, and only in the authorised position.

Working for an unrelated employer, or using the permit for purposes other than the approved transfer, is grounds for revocation. If you want to take a job with a different employer in Bulgaria, you would generally need to apply for a different, appropriate work-based permit rather than relying on the ICT.