Hello marclabru,
It isn't possible to specify additional/convolution reverb within an CODM ODF (or full ODF) -- the only way to do that is via the mixer. There isn't currently a means to send a mixer/reverb configuration to other users, but we do hope to add the ability to import/export/share/copy mixer presets (including reverb configurations) to a future version, as a high priority. In the meantime, you could instead provide instructions to accompany the sample set for the appropriate reverb(s) for the user to select for use with the sample set.