The open canopy pruning method is used on peaches, apricots, and nectarines.
You can prune your plum any way you want to, but you will reduce the amount

I am glad you said that plums can be pruned any way we want to Dwayne,
we have a young plum tree in the garden and two years ago someone let
our old pony graze on the lawn, this she did happily but she also ate
most of the plum tree which was about 3 2 years old at this point, it
hasnt produced anything since and is a very funny shape altho having
said that it has put on a huge amount of growth this year so maybe I
should just let it get on with it and see what happens :-)

kate