hi Nozomi,
In my point of view, "equal" is mostly used in identifying the specific sameness of things or matters as to measure, values or quantity. (i.e. size, mass, volume, numbers, height, grade, point, level, etc.), while "identical" is more of classifying in general the dstinguishable quality or the attribute of the things. In some case, these two adjectives are not interchangeable:
ex: "the rooms are identical except for their curtains." (talking of general and all aspects, the rooms look alike.)
I think if you want to use the adverb "equal" in the above sentence, there must be a little modification in your sentence as to be more specific:
ex: "the rooms are equal (in what?) except for their curtains." (in what? - equal size? floor area? number of rooms?, etc.)
:)