Can I get a video (actually 2) to play continuously over a number of slides?

That is exactly how to to it, using builds to enter and exit the text manually or automatically.

The way to edit the text is to use extra temporary slides to compile the builds.

start by setting up a single text box on a separate slide from the slide containing the video

set the text box position, colour, font and build as you want.

in the navigator side pane, duplicate (command D) the slide as many times as you need text builds in the final presentation. This will ensure the layout is exactly the same in every slide.

edit the text content in all the other slides as needed

copy each text box, into the slide with video, one after the other in the order the build will show during playback.

Duplicate the Keynote file to use for future editing.

Delete the temporary text slides in the original file so they do not display

I then find it impossible to get back to edit the slides again once they have been placed in sequence.

This is covered in my last post, my workflow was specifically created to allow a quick way of repeatedly editing text and also to ensure the build order was correct.

open the duplicated file that contains the text on separate slides

and alter the text on the appropriate temporary slides

in the main slide containing the video, select all the text boxes

(click and drag over the text boxes)

then press the delete key to remove all the text

copy each text box again, one after the other in the order the build,

back into the slide with video. This maintains the build order, the build effect

and timing will be retained also.

You can keep re-editing as many times as you need to.

I thought there might be a simple command that would let video play continously (Through Slides)

Video can only play continuously if placed on a single slide.