My experience has been that you'll nearly always be hit with a change fee to make any voluntary change to a non-ref/non-changeable ticket. I've gone from M to F a few times - always have to pay the fee. ($100 on DL, less on Shuttle, DLX)

The only exception is at the airport - if you want to move from L to K to be able to upgrade (prior to new upgrade rules) - they'd let you pay the change in fare only (if K was available). Same for upgrades to paid F.

In terms of a refund - DL will just give you DL Dollars for the full value of your current ticket if any part of your purchase of a refundable ticket was a non-refundable ticket or DL$. Sadly, they don't bifurcate your refund.

There is a workaround for this tho... which I found accidentally. I had an M/G ticket - needed to make a change - but G wasn't avail on the flight I wanted - so I switched to paid F. Subsequently made 3 more changes to the reservation (being reticketed each time). Ultimately didn't go on the trip - so I called to cancel (to hopefully free up seats for upgraders) and they said "Oh, you're on a paid F ticket - we'll connect you to the refunds department to get this processed." I fully expected DL$ because my original ticket was non-ref M. But, b/c I had so many ticket iterations, I'm fairly sure the rep didn't go back 4 layers to find the M ticket - she just kept seeing F a few layers back.

If you're willing to bet a bit, you could prob upgrade a non-ref ticket to F, make a bunch of changes, then get a full refund. (I've never tried this intentionally - just accidentially as described above.) Worst case, if you lose, you'll just have more DL$.

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One other thing - with the new policy on non-ref tickets becoming worthless for no-shows - and needing to re-book your flights prior to original departure on non-ref tickets - there's a pretty easy workaround to keep your ticket dollars alive and flexible.

Let's say you have LGA-FLL in K - paid about $300 - but now you can't go and you don't know when you're going to be able to go. Prior to departure - call up and change to RNO-SLC one way in Y for some arbitrary date. It's about $300 for that fare - totally changeable (and perhaps refundable if you do what I accidentally did). You'll have to pay the $100 fee - but you had to pay that no matter what. Then, in the future, when you know your travel plans, call up and switch your Y RNO-SLC to the non-ref fare on the route you now want to travel on.

(I use RNO-SLC as an example - there seem to be lots of cheap Y fares in/out of SLC on those shorter flights. LGA-BOS shuttle is a good placeholder, too.)

DL would probably frown on this - I think it's inconsistent with the spirit of their rules - but fully within the letter of the rules (so long as you really plan on flying RNO-SLC in Feb of 04!).