Spec'ing an endpoint that returns different responses depending on params sent

I am new to openapi and am evaluating it in order to spec a REST API characterized by endpoints that return different(ly structured) responses depending on which query parameters are sent to the server. I have been tasked with extending one such API (not written by myself).

For example, let's say an endpoint www.acme.com/gizmo supports 6 query parameters param1, param2, ..., param6. If the odd-numbered params (param1, param3, param5) are initialized the server responds with the XML message <foo>...</foo>. However if the even-numbered params (param2, param4, param6)  are initialized the server responds with the XML message <bar>...</bar> etc.

Frankly, I don't think this is a good design (or is it?) but the API has been shipped and customers are using it.  What I'd like to know if whether openapi can be used to spec such an endpoint.