Yes this is possible and there are a few ways to do it depending on the type of updating you need.
All of these file types can be edited externally via a plain text editor and re saved. The Page would then pick up the text as directed.
Images can be just placed in an external folder and either given the same existing name as one being used or the folder contents can be looked at dynamicilly…
There are many examples on all of this on the site.
Try a search for these…
You get the idea…
One Example for text file loading