Custom SVG in user pallette

I'm trying to get to grips with using my own SVG files in the user palette.

Here's what I've been doing...

I drag and drop an SVG file from my desktop onto a grid on a new user palette. I then select a note in the score, double click on my SVG and, hey presto!, my SVG symbol appears next to the note.

Now, a couple of questions...

Is there a way for me to set up where that symbol appears in relation to a note? I know I can drag/move it into place after I have entered it on the score, but is there a way of pre-determining where it will go (such as a certain distance below the staff, for example).

Also, let's say I use this symbol in 50 places on the score but then I decide "hmm, actually I would like to modify that SVG". Is there a way of doing that? Or do I have to re-import the SVG and replace all the symbols again? Does MuseScore save the SVG somewhere?