I think it might be ok with a solid spacer behind the flat sprocket, are the studs long enough to do this?

An alternative may be to fit a smaller tyre like a 110/80. My Brazil model came with a tyre that size. It made 1st gear pretty much useless on the road. I rec'n it makes it 6% lower gearing than a 120/90 tyre. Whereas a 47T rear sprocket in place of a 45T only reduces the gearing by 4%. Maybe a safer bet. I'm guessing you currently have a 120/90 fitted.

NEWS FLASH - UPDATE
I started thinking of different possibilities after reading your posts (even tho I believe the spacers would work) and came up with a BETTER solution. After using a digital caliper, examining wear patterns on the swing arm slide protector, clearance of the tire & swing arm and just plain a** eyeing the chain from the rear it appeared to me that the sprocket did not need the offset. In fact it appears that the offset sprocket routes the chain outward from the center-line of the counter-sprocket. So I pulled the spacers out and put the sprocket back on. It is now center line with swing arm, chain protector, swing arm protection slide surface and NO clearance problem. And again eyeing the line, it looks better. Rode the bike and NO problems. I will still be taking the bike out next week and again will post outcome. It don't need no stinkin' offset with the JT sprocket! One thing I was taught in Engineering School was look at the data but also trust your observational judgement. The Corvair was really a great car LOL!
rocmoc n AZ/Baja

Sounds like you've got a working solution. I do see what appears to be a 50T dished steel rear sprocket (Sunstar) on Ebay. 16Tx50T gives same ratio as 15Tx47T (3.13).

Hope your observational judgement proves accurate in this case Rocmoc. From what you say I trust it will!

Drove a number of VWs prior to the Corvair. When it came out I was tempted to buy one. Ended up glad I didn't after "Unsafe at Any Speed" revealed its fatal design faults!..
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A Look at Arizona's Mogollon Rim
A Look at Heber/Overgaard

Sounds odd for Yamaha to have got it wrong, how long have they been like this? I'd check with a laser to be sure.

Even if I am wrong we are talking a 1/4" offset over 18" of chain length travel from sprocket contact to sprocket contact, that is approximately 0.014"/one eight inch of lateral movement per link from counter sprocket to rear sprocket. Move your chain and notice how much it can move side to side. This is why the teeth on the sprockets have tapered sides. My CRF450r and other bigger bikes have a chain guide because of the movement of the chain. If I am wrong I will simply install a chain guide. A chain guide would be a simply, effective and no big cost for the ability of using any sprocket. Yamaha engineers didn't give this much thought as they always build in 15-20% safety/fudge factor. You are taught not to design to the edge if at all possible and since this is not rocket science they didn't.
rocmoc n AZ/Baja

Given the explanations you've provided it seems you're on solid ground believing your non-offset sprocket is a non-issue as far as your XT is concerned. You've eyeballed it to the best of your practiced ability. You're confidently on solid ground. No need to worry further about it -- go enjoy the ride!..
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A Look at Arizona's Mogollon Rim
A Look at Heber/Overgaard

First feedback ride report. Friday is going to be a 40-60 mile ride with a trailer pull of 25 miles to the ride location. So I felt a shorter local ride was in order, just in case. Just rode from the house, across the Santa Cruz River up into the foothills. On the lower flat section I easily ran up to 60 mph going and coming. She could go faster as she sound like revs were remaining. Hit the washes with DEEP ruts crashing thu trying to throw the chain if possible, no problem. Pulled thu the sand the best ever. She was fun to ride in the really rough stuff. Not like my CRF was but better than ever excepted. Round trip, a water hazard, sand, deep ruts, ROCKS of every size, off camber and tight turns. Really feel good about Fridays ride. For me the best setup possible, a dirt bike but yet able to ride on the blacktop when necessary. I am running one tooth smaller counter sprocket 14T, and up two teeth in the rear 47T with Kenda 760 tires. I took the Shinko's off as they were too much tire for the XT. Very happy with the little bike now. More after Friday.
rocmoc n AZ/Baja

There ya go! Sounds like you've got 'er dialed in, ready for Friday's ride.

Glad you've got the gearing dialed in and enjoyed improvements. Our bikes were geared 15:58 and we never had issues. Lower gearing, I think, is a BIG advantage riding technical trails.