Is the question mark below allowable...
content="Did your plans change? Learn about our Cancellation Policy.">
I can't find anything that says a question mark isn't legitimate.
No reason why not - any characters within the charset you've defined can be used, and character entities should be used for any others (including " if you need it).
META in HTML 4.01
content CDATA #REQUIRED -- associated information --
CDATA in HTML 4.01
CDATA is a sequence of characters from the document character set and may include character entities. User agents should interpret attribute values as follows: Replace character entities with characters,Ignore line feeds,Replace each carriage return or tab with a single space.
CDATA is the same as normal content text in html -- so anything you can use on your content you can put into your CONTENT attribute.