I don't wish to give too much away and spoil the fun for others but you should concentrate on the down clues which are normal and which should lead you to solving 10a.
The answer to 10a taken with 6a should put you in mind of a severe punishment which will describe the action needed to solve the 10 thematic clues.
Of the 10 across clues which need treatment 5 need
only adjustment by a single letter, the other 5 by 2 letters.
Look out for a couple of Americanisms.