change migx value with ondocformsave plugin

is there a way to change a migx value on save of the resource in the manager?

i'd like to get links to preview images of vimeo with curl (works as snippet)
Now i need to get the migx parsed and on save and foreach row the url filled with the response from the curl calls.

when i do this at runtime it slows down the site massive because of alot api requests and slow responses, thats the reason why i like to make this only once at savetime.