Hi Josh, this should be pretty easy to do - however, because of a bug in Acrobat, it's a two step process:
Open up the document in Acrobat, and bring up the the "Set Page Boxes" tool (either via Tools>Organize Pages>Set Page Boxes, or by right-clicking on a page in the "Page Thumbnails" pane and selecting to "Crop Pages"). Then select to change the page size by using a custom size. Make sure that you select to "Center" the old page on the new, larger page, and specify 9.5"x11" (yes, that's too big, and we will correct that in the next step):
Now apply this change to your tab page and bring up the "Set Page Boxes" tool again. This time, we change the crop box so that only the 9x11" page - with the tab text in the correct position - shows:
To get the correct page size, we have to remove 0.5" from the right edge.
Again, apply the settings, and you should have a correctly formatted and sized tab page.
The bug in Acrobat is that you cannot specify a custom Xoffset in the first step. This would allow us to just resize the page to 9x11" and offset by 0.5" and be done, but that moves the page content completely outside of the crop rectangle, and you end up with a blank page.
I would extract all tab pages to a separate document and then perform these two steps on all pages in that temporary document, and then replace the existing tab pages with the corresponding pages from that temporary document.
I forgot to mention this in my first reply: You can of course also create an Action (or a custom command - see here for more information: Create Custom Commands in Adobe Acrobat DC Pro) to perform both steps with just one mouse click. If you have to do this task on a regular basis, that might be the way to streamline your workflow.
khkremer - I think this might do the trick! I can't get my amended document to the printer just yet but I'm going to make the changes as you profess and mark your answer as THE answer. Thanks for this!