Yep--visits from those not contracted to be in the production they're visiting is common, but when it comes to some desperate for what is guaranteed to be an explosively stupid move from Disney / Marvel Studios (I doubt they would acknowledge why) by having Evans back in that role, whether he's a "prime" or "multiverse variant", when they have their main Captain America who should be promoted beyond one underperforming film with a course correction.
If the Cap role is not portrayed by Mackie, its not Cap.