Hi,
sure it's possible in several ways; using a @ClassBridge (see section 4.2.2.3. ClassBridge in
the reference documentation) you have full control of how each instance is indexed, this can be dynamic and you can change the "index schema" on a per-document basis, or you can even change the full Search configuration on the fly (in newest 3.3-beta only) and redefine the configuration programmatically.
I would recommend though to always index all fields which might ever be needed, and apply dynamic filtering on the results by using
Filters; this way you can hide information rather than not having, useful for when the requirements or rules change.