I think an easy way to address this is to
Not change anything at all. Full stop. No buts, ifs, or 'Well how about's.
I think GW and W40K suck as a company and as a setting. It has absolutely no artistic integrity (Bigger Batman) and it can kick rocks. But NEVER bend the knee to those who see your creative choices as something they can get to control by virtue of whining.
Imagine your eating your favorite food. And then somebody with a gun, takes and points it to the back of your skull and says 'Eat the food or I will blow your brains out'.
Those that say 'Look, you wanted to eat the food anyway right?', are missing the point. The point is the man with the gun sees as having control over you. Whatever he is demanding, no matter how innocous is a demand he thinks he is in the right to make when he is compeltly incorrect.
Now I mean with the gun situation thats one thing, you gotta do it to live. But in this case GW isn't hurting for money and woke mobs move on if denied.
Edit: Yes and all the lore is moronic nonsense. Male Marines is an artistic choice (or the closest thing GW can be too art) and, it should remain that way.
If GW said tomorrow 'There are new Mcdonalds Marines and they are 10 times better then Primaris marines, 25$ a figure please' they would absolutely do it if they could get away with it.