Hmm.
In the first place, the nylon strings for the G, B and E strings at much thicker than their steel counterparts, and substituting them onto a traditionally steel-strung instrument would not mean simply dropping them in.
If your intention of doing so involves your need for less pain when playing the guitar, you could instead work with a classical guitar rather than a folk guitar when starting out.
Also bear in mind that the tuning string posts of folk guitars are much smaller than classical guitars, and since nylon strings stretch more than steel strings, and require more tuning post to tune up, it is not even remotely viable to string up your folk guitar with nylon strings.
I saw one guy do it before, and it looked utterly ridiculous since his tuning posts were bunched up with the nylon strings.