Doing a tt to road retrofit was a very bad experiment for me, but making a road bike into a tt rig was all we had back in the day and it worked very well for *me*. TT to road was that I just didn't like the increased weight bias on my hands being so far forward. YMMV. You can certainly do it though and the only thing that matters is that you like it, not what others think!
Road to tt was all I knew for the first 5 years or so of triathlon b/c that is all we had. I did IM/HIM's on a Columbus SL tubed Pinarello road frame with Scott clip ons for years and that particular frame still holds my 40k tt pr. If I were to get back into tri I would definitely do a road bike with clips b/c I'd never go over Oly. 56 miles is where I'd opt for a tt bike, but not b/c of aero considerations. It would be for a little back relief and overall comfort and the subsequent 13.1.
Road to tt was all I knew for the first 5 years or so of triathlon b/c that is all we had. I did IM/HIM's on a Columbus SL tubed Pinarello road frame with Scott clip ons for years and that particular frame still holds my 40k tt pr. If I were to get back into tri I would definitely do a road bike with clips b/c I'd never go over Oly. 56 miles is where I'd opt for a tt bike, but not b/c of aero considerations. It would be for a little back relief and overall comfort and the subsequent 13.1.