In article ,
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I am now resigned to PVA and skimming this wall all over again, but wondered
if it IS possible to succesfully feather a new skimmed area into a
previously plastered one, or if it's generally accepted that you do the
whole wall.

You can't feather it, but you can cut back the existing plaster and skim
flush with this edge.

In this instance it's not a big deal 'cos it's a small wall and frankly I'm
enjoying the practice, but I had planned on 'touching up' areas of the
living room afterward...

You can touch up with a fine surface filler - make sure there are no
high spots before you fill, minimal sanding should be required to get a
flat smooth finish.