Simply replacing a video will be easier than trying to edit it. There is no way to mesh video of single ASL signs that is commonly available to all. Making a picture bigger or smaller does not change its content and information. To edit the picture, i.e., make it express something slightly or greatly different from the original, requires it to be replaced in a wiki.

The 4th grade level readers (and those slightly above and below) will be able to find the article on a topic they are interested in by searching just like any other user. A single or multi-word search is not curtailed by the users reading level unless they are totally unable to read and write. The "average" user can then attempt to read the English text if they like and see the ASL video which they will have a better chance of understanding. Thus their trip to the article has allowed them to gain knowledge via ASL and perhaps helped them understand the English text a bit more via the ASL support provided