Prevent bleeding when Gaussian blurring a selection?

[rich2005]

Throwing one of the procedures into the hat - no idea if it works inside a game engine.

Use a path to define the selection. Path to selection. Copy the selection. https://i.imgur.com/LVQePTR.jpg

Edit -> Paste As -> New Layer In Place. Gets a new layer of the area. Lock the alpha channel and gaussian blur. https://i.imgur.com/aI6VCPr.jpg

Check before merging layers https://i.imgur.com/tDrfFkt.jpg