Hi Matt,
Decibel uses an eVar for it's integration for two reasons.
1) Allows sessions in Adobe to be associated with Replays/Sessions in Decibel.
2) In order for Decibel to be able to use Adobe Segment data.
In order to fulfill both use-cases, you will need to use an eVar. The eVar can be set in a number of ways:
1) Default - Decibel can automatically populate the eVar when it loads.
2) Manual - You may set the eVar yourself, via Launch or your TMS and using AppMeasurement.Integrate.
With this in mind, you could switch to using the Manual request type, which would stop Decibel setting the eVar itself, and allow you to do it in your own way. This would allow you to then set a prop or whatever else you may like to do.
Please note that in order to be able to use Adobe segments in Decibel, you will need to use an eVar.
Thanks,
Marius