Alloy, a Substance Painter plugin that converts Metal/Roughness ⇄ Specular/Gloss instantly, right inside your existing project. No messing with layers, channel manipulation, or manual efforts of properly masking different workflows required.
One-click setup, can swap shaders instantly to preview results, and including correct texture export presets for both ways.
Built and shared for free; try it out, and pass it along if it helps!
https://www.artstation.com/marketplace/p/Gr3dv/alloy-pbr-workflow-converter-filter
Specular to Metalness conversion:
Fringe correction on newly converted Metalness:
Metalness to Specular conversion: