Controlled Impedance Trace-reference plane Placement
If you have this stackup - controlled impedance track, signal track, reference plane, where the controlled impedance has been calculated assuming the signal track isn't there, then the signal track will do two things

Reduce the impedance of the top track in its vicinity and
Couple signals to/from the top track

If it's just one signal track, then the reduction in impedance will only be over a short length and may be negligible. If the top track crosses the signal track at right angles, then the coupling of signals will be fairly small, and you may get away with it.
If you have a whole layer of signal tracks, then the impedance change will be significant. The top track will couple all the signal traces to all the others.
However, this pontificating what the effect would be if you were to run a signal layer between a controlled impedance layer and its reference plane is really a waste of time, because it's something you don't do. You never need to do it. If you feel the need to do it, re-order your stack up so the signal layer is below the reference plane. Or if you do it, you haven't got controlled impedance traces. .