The copy / paste function in PaintShopPro does not require the image to be saved, so after a resize, all that's needed is a second copy...I guess that makes it a copy / copy / paste....
It seems the basic functionality for 'nice access' to external programs is already available, albeit not intuitive nor without manual setup. For example, I've found that any significant number of 'full-size' screenshots (say 10+) slows the page display down significantly. My solution is to use the URL field with "file:///c:\\myscreenshots\mymovie\" where the 'mymovie' is a directory that contains all the screenshots (or people images, as the case may be). When I click on the url, file explorer fires up with the specific directory named.
I suspect that a jpg image in the url field would cause the registered viewer / editor to open the image (untested). If so, the basic mechanism is already there, and all that's needed is a bit of refinement to make it usable. If not, the option exists to use the path and name of the program in the url field and have the image / directory passed as an argument.
As far as that goes, many image editors have a command-line parameter set that could be invoked which could provide things like batch updates (resize, add a frame, sharpen, auto-enhance), which could be an interesting way to provide features that need be configured only once and would be specific to a user...esp. if the files are stored outside the database where access is easy. PVD from my testing will simply load the image, without regards to any changes (other than file path and name).
ImageMagik (sic?) provides a command line interface to an extensive set of imaging processes that could be invoked by a batch file in the url to do very fancy things.