We have a few services that are connected to our domain through SAML and some other sync tools. We are looking at adding custom fields to the AD Schema to hold the data for these services (fields for primary group for a few services, separate fields for preferred first/last name, multi-entry field for e-mail aliases, etc...)
I would like to avoid using existing fields as they don't describe their contents and are finite.
I couldn't find any information regarding best practice for adding additional fields, other than a few warnings that it may break compatibility with upgrades. I have been able to add additional fields to the schema in my test environment and I didn't notice any issues, but I'd like to avoid stepping on any landmines this might bring down the road.
My main concern is that if I extend the schema I won't be able to raise the forest/domain operational level in the future when the schema is updated. Is this the case? Are there any best practices or common gotchas in regards to this?