Interesting idea, Tickerguy. I wasn't aware an H9 conversion was possible. After watching a couple of YouTube videos on how to do this, it looks like it's only the bulb that needs to be modified, while the stock headlamp housing and connector remain fully intact. That makes this upgrade instantly reversible, with no ill effects if you want brighter light output but don't want to go with HID/LED.
While the conversion would work for the Mazda 6 low beams (which are H11), it looks like this mod won't work for the DRL/high beams, which are 9005 bulbs and are in a non-projector housing. In the foreseeable term, switching to a whiter bulb like the Crystal Vision might be the only feasible option to get less yellow output. Having said that, since in the DRL position, the bulbs are being driven at 50% voltage, even the whiter bulbs may look more yellow than they should. On Amazon, people are complaining that their upgraded DRLs look at yellow as stock.
No, it DOES work for the DRL/highs; you don't NEED a front glare shield on the highs (there isn't one on the 9005 in fact) since you never (I hope!) use them in the presence of oncoming traffic (they'll blind you anyway, upgraded or not.) The higher-output sub for the 9005 is the 9011. The DRL circuit underdrive is at a low enough output that you won't be able to tell the difference in DRL mode between 9005s and 9011, so there's no glare problem during dusk hours either.
Both require no change to the housing or wiring; the H9 requires you grind off part of one of the bulb locking tabs and a key in the socket (on the bulb); the plug on the car remains unmolested and mates properly. The 9011 is connector-compatible and requires only part of a tab be ground off, and the tabs on 9005s and 9011s are both plastic so it's easier than with the H9s!
Again this is not "street legal" or DOT approved, but in both cases you're replacing a bulb with one that has the filament of the same size, in the same place and orientation (thus will produce the exact same pattern) and it draws a similar amount of power (identical in the case of the 9011 .vs. 9005.) The difference and reason for the higher lumen output is that the filaments in the H9 and 9011 burn hotter and are more efficient, thus emitting more light (and about the same amount of heat) but last about half as long as the H11 or 9005 (nothing's free!) And again, as in the case of the H9, you do NOT want to buy any of the "fancy" or "uprated" 9011s (there are
both "counterfeit" and other screwball 9011s out there and just like the 100W H11s they will likely melt your housing, the wiring or BOTH *and* may not have the correct beam pattern -- so don't try it!)
And just to say it again, do *not* do this with the factory halogen fogs (or for that matter in any car with non-projector lowbeams!); those use H11s but absolutely require the front bulb paint or they will glare like crazy and blast oncoming drivers, and the H9 bulb doesn't have one. If you want upgraded fogs the best option is the Morimoto LED model; they have the correct bar pattern and don't blast oncoming drivers, are very bright but sadly aren't available in a yellow-colored version - they're sunlight-white in color temperature.
If you're going to do this conversion use the standard, off-the-shelf bulbs from a reputable supplier (Philips is a solid brand that produces spec-compliant products and you can get them on Amazon.)
Here's a link to someone who walked through it on the Toyota 4-Runner, which uses the same bulbs the Mazda 6 does. The 6s low beams are projectors (I don't know if the Toyota 4-Runner is) which means there's zero issues with glare on the lows, and of course for the highs it's a non-factor because you already have an unshielded-tip bulb in there and don't run highs when there is oncoming traffic anyway. How To: Headlight Bulb Conversion (H11 to H9 & 9005 to 9011) - Toyota 4Runner Forum - Largest 4Runner Forum