wiper blades covered under maintenance plan?

actually, you don't need to remove the blade and you don't need to remove the metail strips. your version of the process is overly complicated. simply give the blade a tug on the end with the locking tabs and it will slide out the rest of the way. slide the new one in (being careful not to let the metal strips fall out) and when you reach the indent/locking tab, give it a little extra tug to lock it in place. that same style of blade is OEM on many cars.

Will any of the aftermarket refills work? Or must I buy the refills from the BMW dealer?

the auto parts store i went to last week had a little computer... you punch in the year, make, model of your car .. and the computer tells you which blade refills fit your car

just replaced the wiper blades on my dad's lexus
pulled the rubber blade and the metal spines out ... then replaced with the refill...
not too hard
took like 5 minutes and got my hands a little dirty

At my request, the BMW Center replaced the wiper inserts after one year. The replacements skipped and danced accross the windshield. The service writer explained that the glass needed to be squeaky clean, otherwise the wipers would skip. Interestingly, I cleaned the windshield until my arms ached and the blades continued to perform Saint Vitus dance on the glass.

A second replacement at no cost solved the problem.