If you wanted to scale the content to add bleed then you would use 2 resize operations.
Resize to 102% while resizing all PDF boxes and scaling the content
Then resize the trimbox to 98% while not resizing other boxes and not scaling the content
If the document has bleed content that's not visible (which is what I think you are describing) then that's pretty trivial.
Use Resize to push out the bleed box (other boxes are automatically adjusted to ensure proper nesting)
The key is to uncheck the option to adjust other boxes and to set the content scaling to none.
What I like most on the new version of PitStop Pro, it has the ability to extend bleeds on a file that has hidden bleeds. What I meant by this is if I have a letter size document as an example and I don't have a bleed visually from the file, all I do is go to my global settings of PitStop and perform an extend bleed and clean up trim area. The file then will automatically make a 1/4 of an inch around bigger than letter size and the bleeds have been extended without physically massaging the file itself.. Do we have the same capability in Core or I just don't know how to find it ?