I assume you mean warm season grasses, since cool season grasses will have already bloomed.

The foliage will continue to grow on trimmed warm season grasses, but it will have squared-off ends, which will be browned where they were cut. If you don't take more than 50% of the foliage length, chances are the plant will still bloom, and the blooms will be at their normal height, although the foliage will be shorter. I've cut many Miscanthus clumps halfway down, divided and re-planted them in late spring to early summer. They look awful the year it was done, and you can't tell anything happened in the next year.

This doesn't apply to early summer blooming warm season grasses. Chances are, you'll trim off the flowering stalks on them. They still might throw up a few blossoms, but nothing like normal.

Thank you for the quick and helpful reply. I gave my friend in WI the information and she was able to come to a decision about what she wanted to do. You wouldn't think there is a world of difference between zones, but there is! Thanks again.