Thus, to add your calls above, the block of text to paste into the User Scalable field would be:
This might make it easier to see what's going on... Sam's original code insertion block:
In Axure, select Publish > More Generators and Configurations..., select HTML 1 and duplicate it:
In your new generator, paste your code into User Scalable (no or blank):
Click Generate and test it out.
Now, for your other question...
If you publish to Axure Share and use the Plugins feature, you can assign the plugin (apply the external .js and .css) to only specific pages. This is your best choice.
If you can't use Axure Share, I don't know of any way to select multiple generators for one prototype.
Here is what I'd do, though. I would create a second prototype for the "one page" and generate it with my custom JS-CSS generator. Then, back in my first prototype, that page would be blank with an OnPageLoad : Open < link to my second prototype > in Current Window so that it redirects to my special page. Then, when my special page needs to go to another page, use a link to the first prototype. Make sense?
Another approach would be to publish the second prototype with the one special page, but in the first prototype, put an Inline Frame widget on that page and call the second prototype to load in that inline frame.
Some general notes on this...
You will need network access to your external .js files or it won't work. Seems obvious, but it can trip you up if you are testing outside a company firewall or that server is down, or you are testing remotely and your usability lab's wi-fi is down... all the things that shouldn't happen but do.
This works with the Preview (F5) as long as your custom generator is default, or you choose it from Publish > Preview Options (Ctrl-F5) > Select the HTML configuration...
(Oh, by the way, you can include code samples in your posts by using the Preformatted Text button in the editor header (used to be called "Insert Code" in old forums. That's what I did above.