I have a hollowbody electric guitar on which I put some ball-end nylon strings as an experiment and tuned to by preferred tuning (G-D-d-f-g#-b). I really liked the distinction in sound between the "boomy" wound strings and the "harp-like" unwound strings, but would like to have the fourth string sound match the upper four rather than the bottom two.
I've purchased a second set of ball-end strings and put the third string from that second set onto the guitar's fourth string (tuned down a minor third from its designed pitch) and it sounds good, but since it's tension is only about 2/3 that of the third string it's a bit "floppy".
Steel string sets publish the gauges of the strings included, and within a category of strings one can usually figure that tension is roughly proportional to the square of the gauge (wound strings of a given gauge are looser than unwound); I've not seen such figures published for nylon strings.
Are there any recommended approaches when selecting nylon strings for alternate tunings? I would guess that combining strings from a few different sets (my guitar seems amenable to either ball-end or loop-end) would be the best approach, but I don't know different strings in different sets would compare, or whether the strings from different sets would have similar sounds.
Even though nylon strings aren't terribly expensive, they do have a significant break-in period, so it would be helpful to figure out a good combination of strings without having to try too many different ones.
I don't have a huge desire to file the nut or the bridge on my guitar, but even with a stock set of nylon strings I'm happier with the way it plays than I ever was with any other strings I tried it (for either standard tuning or my alternative one) so I don't particularly expect to go back to steel strings with it. If the best unwound string for the fourth spot would be larger than an ordinary steel 4th string, I wouldn't mind committing the guitar to such usage.