If enough of us - fortunate enough to have decent credit - went in and bought armfuls in various sizes to try on at home then return it all just within the time limit and state clearly at the tills that we’re not comfortable with mixed sex changing maybe that may be an effective protest??
I know that this would be well-intentioned but please don't: it would just create more work for shop staff, who don't have any say over policy.
But the idea is to make not more but different work for the staff. If the staff are so busy handling returns, they cannot handle other duties: reshelving, inventory control, other customer service, etc. Diverting their workload into handling returns hits at the overall productivity of the store, which is exactly what you want the store to feel and where you want them to feel it: in the wallet.
Believe me, stores pay close attention to metrics around productivity. Retail margins are very thin. It takes little disruption to create large effect. So far, it’s the transactivusts who’ve created small disruption with large effect, by merely making complaints.
In the world of retail, though, there’s not a single demographic with more power than women with families. Primary has put leverage in women’s hands. All women have to do is use it.