A replacement-musician app could help a band fill a specific role for a particular performance. Useful details include instrument, repertoire, rehearsal expectations, location and the agreed commercial arrangement.
The band needs a way to review suitability before accepting someone. Sharing charts or private event instructions can happen after the relevant approval. A replacement request should close once filled so other musicians do not keep applying for an unavailable engagement.
Pilot within a defined musical network and make cancellation expectations clear. Test a musician withdrawing after acceptance and a change to the performance time. Profiles and examples can support a decision, but the app should leave musical compatibility and final engagement approval with the people organising the gig.
Related reading: ListnIN: How a Live Music Streaming App Connects Artists and Fans.