I’m not clear on exactly what you want to do but…
Did you render a 500 frame animation that you want to pause at different places (5,10,20 secs etc)? You would import the image sequence as a single strip then cut the strip using HARD CUT at the points you want to pause at. The Hard Cut function allows you to stretch out the last frame as a still image.
Or if you are changing the content of the images-
If you have 2 groups rendered images, that have corresponding same names, then you could swap their folders around. That is have one group in a folder called ‘online’ and the other in a folder called ‘offline’. Then swap the names of the folders. As long as the file source names are the same Blender will just substitute the new swapped ones.
Alternatively you could try using the VSE extras addon which has a strip copy function. But I’m not sure you will get all attributes (like length) copied?