I've just restrung a cheapo nylon strung guitar. It was given to me for free because of a split between sides and top, an easy glue repair, and it needed a new saddle. So all the strings came off for the new saddle. However it reminded me that there is a convention when restringing classical guitars of trapping string ends at the bridge under adjacent strings. The first string end goes under the second string, the second string end goes under the third string, etc, until only the sixth string is left. This dictates the order that strings are put on and also the order they are taken off. It also means that all the strings have to come off before any can be replaced.

Of course all this only applies if you are using the basic plain strings. These days you can buy ball end nylon strings and all that complicated tying at the bridge is not needed and you can change ball end strings one at a time and in any order.

If GSS was referring to plain nylon strings which tie onto the bridge then remove strings bass to treble and replace them treble to bass.