My opinion to achieve what you want.
I don’t know the size of the driver, so a 15mm Mtnelectronics driver with 4 7135’s might work or 17mm with 4 7135’s removed filed down if its 16mm.
I think 4 7135’s will work with a nichia or samsung led in a high CRI to get you to the 500 lumen mark. 4 7135’s will give about 1400ma except on the 17mm driver, 4 will give about 1490ma. Its possible with the 17mm driver only 3 7135’s would be needed to reach 500 lumens depending on the led you use. I prefer the Samsung 4000k LH351D 90 CRI. The drivers from Mtn have different UI’s you can chose from.
If the D25a is your chosen size light but lacks other features, then modding it should get you your holy grail. 
For most of us modders that’s the whole reason we do it, we can’t buy a light exactly like we want it. 