You can do an MVC override in the backend views of K2. But I wouldn't recommend it.

Here's basic stuff you should know for MVC overrides in Joomla: docs.joomla.org/Understanding_Output_Overrides

If it's the backend and you change it a lot, on subsequent updates, changes in CSS or JS may cause your copy to break.

If you refer to the frontend editing form, you are free to do more things there of course, but do keep in mind that the same rules apply in terms of future upgrades & functionality.