Yes, Hale you can and coincidentally this is also the easiest way to do it
Edit your replay normally up until you want to strike Uke out of the freeze then save it
Open in notepad and just paste in Ukes info from the frame you want him to freeze on every single frame, you will have to manually write new frames but that's really simple.
For example in a 1000 frame replay if you want to freeze Uke on frame 400 and punch him out of the freeze on frame 300 you'd do this:
1. Make sure you move one of Ukes joints on frame 400, this creates the information about Uke which we will paste in later
2. Keep editing normally up until frame 300, disregard the hacking part which will happen 100 frames earlier for now, just move your tori into position and stop on the frame where he will strike Uke OUT of the freeze
3. Save replay, open in notepad. On frame 600(inverted from 400 because we are now working in notepad) you will find information about Uke, copy this.
4. Now begins the laborheavy but simple part, on every frame between 600 and 700 you will paste in the information about Uke AFTER Toris information for good practice and to make sure it doesn't hiccup.
5. After saving and watching the replay you will notice Uke still falls out of the air but teleports back into "the freeze position" every few frames, this is because we only pasted in his information on the frames we edited Tori on. Gravity still pulls on Uke on the other frames.
6. Go back into notepad and manually add all the missing frames between 600 and 700. Just write Frame 601; and the paste in the information about Uke again. Then carry on with Frame 602; and Frame 603; and so on. Skip the frames you already pasted Ukes information into in step 4. Do this until your last frame, save it, open the replay in Toribash and you will have a perfect freeze!
This is also the solution to your question Denilumi, this process is the only way to do that.
Important to remember if you are new is that Ukes variables always have "1" as a suffix and Toris always has "0".
IE POS 1; belongs to Uke and POS 0; belongs to Tori
Hope this was helpful to someone, this is actually a really good practice to get a basic grasp on how Toribash renders replays and it's good to see people engaged in hacking :D