Just turn off texture combiner mode switching to GL_MODULATE for that unit when you’re done and you’ll probably be good to go.
Code using combiners after you shouldn’t be making assumptions about the state of the inputs and operators unless you have to cooperate with some other software that tracts state in app code in which case defaults won’t cut it.
I sure wouldn’t set combiner state relative to the default setting, that’s just asking for trouble.
The default environment combine mode is modulate, as is stipulated in the spec.
If the particular bit of information you seek is not detailed explicitly in the spec, then it is likely an implementation detail; and in such a case, there is no specified default behavior to rely upon.