Noem and Bovino have always insisted they were conducting a "targeted operation to seize a violent criminal", so is this a real change, or PR?

It will probably be a real change in Minnesota. There has long been a schism within the Administration on what the immigrations strategy should be WRT non-criminal illegal aliens. Noem and Bovino have been in the "get everybody" camp, while Homan has leaned more towards "target the worst ones" camp.

Here's the thing to remember - the "enhanced operations" in Minnesota weren't going to make those communities safer or get more violent criminal aliens out. If they were designed to do that, and effective in doing that, then they would be going to red states or to communities that have larger numbers of illegal aliens. Red states would want them if they were good for the community, and the Administration would have doled them out as rewards for supporters rather than punitively against communities that didn't vote for him. And if they were good at catching a larger proportion of aliens, they would have been deployed in the areas where there are vastly more aliens (like Texas or Florida or Georgia or Arizona).

Because of how they were deployed, we know that the "enhanced operations" were intended to serve purposes other than catching a lot of unauthorized aliens. The Administration seems genuinely convinced that these tactics are not achieving those intended effects - or at least are causing enough backlash that it's not worth continuing them in this manner.

If they only arrest actual criminals, instead of every brown person who doesn't have his "papers" on him at the moment, how are they going to generate the big numbers that MAGA wants to see?

Well, that's the question - is this just a change in tactics in Minnesota, or nationwide? Minnesota doesn't have all that many unauthorized immigrants. It's not even in the top 10. The national numbers are going to be determined by what ICE does in CA, NY, FL, NJ, IL, NY, and the other states that have much larger unauthorized populations. If ICE nationally were to start targeting their operations to only immigrants with criminal records, they are not going to be able to generate the big numbers of arrests that MAGA wants to see.