If they really wanted to change regulations they'd push changing zoning regulations in cities to allow building anything other than detached single family housing. That would be totally reasonable and help alongside tax incentives. But I have a feeling that's not what's meant by changing regulations...
I thinks that's one of those state's rights things where federal government can't just tell a town how to zone it's own land unless they're taking it away from the town like for a national Park or something.
The best way to change perception of mixed use residential areas is having people live there.
The bigger issue is that these buildings don't work by themselves. The biggest issue with suburbia is car dependency, which can only be countered by walkable cities and public transport (both of which require higher population densities)
Before you can start to change public perception it needs to be legal to build densely. Parking minimums and a variety of other commercial building code regulations make this much more expensive in the US, all while the people nearby in single family homes fight any new builds due to their poor perception of condos and apartments. Just removing the stigma is only one part of the equation.
My perception of dense housing is smelling cigarettes and weed and hearing fighting, dogs barking, loud exhaust, and loud bass for hours on end.
I think we change the perception by enforcing rules to keep people from disturbing others peace at home. Make it a reality that dense housing isn’t a worse experience. That isn’t currently the case.
I’d be much more apt to go back to dense housing if I was confident that my complaints would be heard and actioned up to and including evicting the offenders (after many complaints and no corrective actions taken). But I have never heard of such a place.