From what I've heard, third party contractors in Houston are a bit above the $12/price, but it is somewhat in line with what developers pay before concrete prices spiked before COVID.
They do still have to get approval and meet criteria to pay the $12/sf fee, so it isn't completely discretionary on their part. Currently the city is approving a few hundred sidewalk modifications per year that haven't been paying anything more than the $1000ish application fee.
Exactly, they can modify it. Time will tell home much they'll be able to do, though.