If there are single fixture bathrooms they can be designated as gender-neutral provided the gender neutral rooms come from both the original male and female counts.

248 CMR 10.10 (18)(r)

Use of Gender-neutral Toilet Rooms. For purposes of the minimum fixture requirements of 248 CMR, wherever 248 CMR 10.00 requires two or more toilet fixtures designated by gender, those facilities may be replaced with single use Gender-neutral toilet rooms pursuant to one of the following options:

1. Every gender designated toilet fixture is replaced with an equal number of single use gender-neutral toilet rooms (such that there are no gender designated fixtures); or

2. Where the code requires four or more toilet fixtures combined for males and females, gender designated fixtures may be replaced by single use Gender-neutral toilet rooms in increments of two such that for every male designated fixture replaced by a Gender-neutral toilet room, a female designated fixture must also be replaced by a Gender-neutral toilet room, and vice-versa (e.g . instead of three men's toilets, four female toilets, there may be installed two men's toilets, three female toilets, and two single use Gender-neutral toilet rooms).

The sad reality is that Massachusetts plumbing code does require separate facilities for male and female. You might see some nonconformance to this rule because interpretations and enforcement of the plumbing code is left to local plumbing inspectors, and there is surprising divergence on what they allow in their towns.