Blender 4.2 or later; development and verification are done on Blender 5.1. On the Unreal side, Blueprint generation targets Unreal Engine 5 and needs the Python Editor Script Plugin enabled — it ships with UE5, you only have to switch it on.

Partly. The naming preset covers Unity conventions (SM_ / M_ / T_ with _BaseColor, _Normal, _MetallicSmoothness, _Emission), and FBX / glTF / OBJ export all work as usual. The assembly scripts that build a Blueprint are UE5-only — there is no Unity-side counterpart.

It repacks UVs, so a look that depended on the accidental placement of UVs will change — that is a property of atlasing, not a bug. For atlas-bound assets, unwrap properly and paint colors deliberately and the look survives intact. Transparency is not preserved in atlases either (baking is Emission-based, RGB only), so export transparent parts through the normal path.

No. Exports are non-destructive: material swaps, temporary moves and copies are always restored afterwards, Apply Modifiers works on the export copy, and atlasing cleans up its temporary meshes and images by reference so the .blend does not bloat. Export operations also refuse to run outside Object Mode, so unsaved edits are never lost.