Another alternative is to use a new property that makes activity unambiguous. For example objectType: Reply.
This way we can define it once and not worry about the proliferation of AcceptX activity types.
This technique was used by authors of VC Data Integrity spec to solve a similar problem with proof types. They provide the following justification:
One of the design patterns seen in Data Integrity cryptosuites from 2012 to 2020 was use of the
typeproperty to establish a specific type for a cryptographic suite. …
This led to a greater burden on cryptographic suite implementations, where every new cryptographic suite required a new JSON-LD Context to be specified, resulting in a sub-optimal developer experience. …
Authors creating new Data Integrity cryptographic suite specifications SHOULD use the modern pattern — where thetypeis set toDataIntegrityProof; thecryptosuiteproperty carries the identifier for the cryptosuite