Scenario using Glyphs 2.4.1 (948) beta:
Several glyphs using _part.line as a Smart Component piece.
Second instance that uses Rename Glyphs to swap in a different _part.line.newstyle for _part.line.
Result is that only the glyph with _part.line set with properties at default get swapped in. Glyphs that have _part.line properties set at other values don’t change. That seems like a bug.
.glyphs file: part-rename-export.glyphs.zip (914 Bytes)
Instance using Rename Glyphs
I would have expected the direction of /B and /C to change.