TextMate 2 still does not have any replace action. It’s replace all or copy and paste. I really want to get back to using TextMate as my main text editor, but it doesn’t look like that’s going to happen any time soon with glaring omissions like this.
There will be a Replace action at some point. For now you can put the replace string on the regular clipboard and alternate between ⌘G (Find Next) and ⌘V (replace match)