Perhaps an odd question about a modern flashlight, but I haven't been able to find an answer anywhere.

I'm considering getting myself an incandescent Mag-Lite, but since 2012 they use a proprietary bi-pin bulb that goes in a little plastic holder and then into the flashlight. Does anybody know if the bulb and its holder can be replaced with a standard PR or KPR bulb, or did they redesign the flashlight itself to make that impossible?

Check on mag-light website and see if adaptors are available-or LED conversion kits.For portable lighting I went away from Mag-Light since their designs are now rather dated.Olight is a good alternative.For portable lights--expensive-but worth it.Go Polarion I have their PS-PH50D light.Has a HID bulb and two light settings.One of the more powerful and long lived HID single bulb portable lights out there.They cost about 2 grand-but LOVE mine--used everyday!!!can generate 6,000 lumens of warm-white light!!!You buy this-cry only once on its price.Olight is a much less expensive alternative-there lights are LED.The Polarion is the most liked and reccomended light by portable light enthussiatsts.

There are adapters to put bi-pin bulbs in older Mag-Lites, but not the other way around. But there are also third-party LED bulbs designed to fit both the old and new Mag-Lites. So I'm just wondering if standard krypton bulbs also fit the new units. I'd like to know if I'll be able to drop in any standard bulb if I wish, or if I need to find an old Mag-Lite on eBay.

I'll have a look at my new Mag-lite and see if the adaptor can be removed. 

I've just had a look and although the locking ring round the adaptor unscrews I don't want to run the risk of damaging the torch. 

Have you tried contacting Mag-lite directly and asking them if it's possible.? 

Extensive discussion can be found on Candle Power Forums.  Short answer is no: the late Maglite incandescent C and D cell torch design, exclusively holds their bipin lamps.

I wouldn't mind that, I would enjoy buying refills of those nice Xenon light bulbs, but: as far as I know, Maglite only sell replacement lamps as individually-packaged retrofit/upgrade kits.  It is appallingly wasteful: garbage plastic packaging (store peg plastic hanger card), plastic+metal lampholder (bipin socket to PR flange base adapter), and retaining/cap ring/nut, comes with each and every single little lamp.  Disgraceful.

edit add: For those not familiar with contemporary incandescent Maglite, here, see how wasteful is their lamp-bulb package.

Hmm I have a older 3D Maglite and yeah it just uses regular flashlight bulbs. I did replace with one of the Maglite produced LED lamps though.

Those newer Xenon bipin lamps look nice but it does seem pretty silly that they don't sell the lamps separately. I have a older Maglite so I do need the additional parts for it but I don't need them for subsequent replacements. Even the bulk pack advertised includes all of the lampholder parts too. 

Yes, you can remove the bi-pin lamp and adapter and install a PR-based lamp. You just have to either drill out or replace the lamp retaining ring. The lamp retaining ring that comes with bi-pin flashlights has a hole in the middle that's too small to accommodate the larger PR-based lamp.