i haven't completely tried it, but here's what my >own< singular brain cell knows:
1. upload the template as normal
2. click on create meme again
3. select your template
4. move text boxes to the location you want them to and set up their apoearance
5. you should see a button with "save text box settings" or something like that, click on it, it should do what you wanted, as you described above
6. next time you or another user uses your template it should now have the updated text boxes