I get where Festool is at with the warranty,.... tools have cords, etc... and it makes perfect sense to me.
However, I have to agree as inferred up-thread that there is a bit of 'common sense' ambiguity in the matter.
1). If one buys a TSx5, which comes with a rail. It has always been crystal clear (to me at least), that if you don't like it you can return it during the 30 days for a "FULL REFUND, No questions asked". I have never seen it suggested or implied here that one would be 'stuck' with the 'consumable' rail and the refund being ~$100 less.
2). If one buys a MFT/3 which comes with a rail. Again, it has always been crystal clear that if you don't like it you can return it during the 30 days for a "FULL REFUND, No questions asked". I have never seen it suggested or implied here either that one would be 'stuck' with the 'consumable' rail and the refund being ~$100 less.
In both of these cases it would be a very realistic assumption that these rails will have been used and their splinter strips cut, but yet a return on those rails would be deemed completely acceptable in both those instances.
So with that said, I would find it a bit `chafing` if a dealer would not allow a `return for "upgrade"` (in a reasonable time frame), since the OP was really asking the dealer if he could spend a little more money at that store if the dealer would help remove some of the 'hate' from the first rail purchase.
For the dealers out there that read this, I think this would fall under the category of "Selling Service". From what I am reading here in this thread, it is well withing your prerogative to refuse a return on the rail. Fine. [read that in the same manner that a woman says "fine".

] The customer has the prerogative to buy the longer rail elsewhere. It is stories like this that will separate 'the wheat from the chaff' when it comes to the Festool dealer network. Which dealer do you wish to be, the wheat or the chaff?
Presuming all margins being equal in terms of percents, would there not still be an increase in real profit by taking an otherwise re-salable rail back, replacing the strip then selling the customer the longer and hence more expensive rail he truly wants? In doing so a dealer has created a happy and infinitely more likely to return customer, as opposed to the long list of unhappy customers that have done business with one of the two chains that we have numerous threads bad-mouthing. [2cents]