Unable to switch from a single house exterior to multiple pieces

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Date & Time: November 6, 2020
Frequency: Always
World name: Leviathan
Character name: Feral Savage
Retainer name: N/A
NPC name: N/A
Monster name: N/A
Class/Level: N/A
Party or solo: Solo
In-game time: Not sure
Area and coordinates: Ward 15, plot 15 Mist, Leviathan
Housing: See above
Steps:
1. Have a single exterior design on your house (in my case it is the weapons outfitter design).
2. Want to switch to individual pieces like a Glade Roof and Oasis Walls or any combination (I tried with several different ones)
3. Preview does not work, and when you click Confirm, it says "Unable to Confirm"

I'm on PS4. Not using any peripherals.

"All in one" housing exteriors can't have any sub-part added to them.
In-order to make a multi-piece exterior, you have to remove the "all in one" exterior completely and then add all the required sub piece exteriors.
In other words, you can't take a Weapon Outfitter house and change out the roof or walls, you have to remove the Weapon Outfitter exterior completely, and then build up the exterior with roof, walls, doors, windows, etc.. Of which you can mostly mix/match within restrictions of the particular housing district and plot.