You mean can you pay MORE to Disney for tickets that you may (or may not) ever come back to use in the future...
but if you DO you'll spend even more money to buy more things at WDW than you otherwise might not?
What if during your vacation you realize you won't use all of the features of your tickets - for example the water park options - can you change them to no expiration mid vacation?
Yes you can as long as you do it within 14 days of first use of the ticket. The fee to add the no expiration will be based on the original length of your ticket, not the number of unused admissions remaining when you add the option.