Like the Twilight Forest, custom dimension portals shapes, portals are always same Nether portal doors, When creating the dimension, An option to make the portal look like Soil instead of a wall, Can just use the End portal Model,(or create model)
But am sure it can be done using procedures (a lot)
Issue comments
In the procedure maker i could not found a "load dimension [select dimension]" or something. Maybe if you would just add this option, it would be possible to create a custom portal block which has a procedure: if player collides with block, and now the procedure which loads the dimension. The needed portal could to be a structure of any shape now which can be spawned with item ot whatever and ...done. i guess... ^^
A similar ticket was opened recently: https://mcreator.net/tracker/issue/47850
We use the vanilla portal code for now as implementing custom portal structuring, spawning, localization and placement detection is out of the scope of the MCreator.