definately this could work, but your adding in alot of stuff and your AFOV will not be the same, i thought about this idea a fair bit when playing around with Starry nights pro 6, i entered all my eye piece combinations in with all my barlows and what was surprizing that you got the best FOV from the eye piece alone and plus you would have to have a good formula to figure out what eye piece you would need to get back to your original magnification
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If your seriously into visual and you have a fast newt aka <f5 then bite the bullet and buy a paracorr. they are tuned for visual use with adjustable top to get the distance from the lense to eyepice correct.!
Just like Photography, we need to get a MPCC or else your photos look like your heading into warp travel!