I play concert size, and don't play Low G, because I don't like wound strings. Mainly, harder on frets. They feel and sound different, and don't last as long. Defeats what makes regular strings more attractive.
I usually have to replace an A string before I have to replace my wound string, so although I'm not a heavy player I tend to replace separately. But I'm not a good or knowledgeable player at all so who knows!
I am a devoted low G player who uses wound strings for G and C. Even though the wound strings theoretically should become dead sounding sooner (because of crud build up) I change the whole set. I can usually get 8 months or more between sets, even on heavily played ukuleles. Compared to steel string guitars that need changing ever month or two it's cheap insurance for good sound
Unless I’m experimenting between high/low G or a mix of different strings on a particular uke, I just change the whole set. Then less variables to consider as a function of tone and feel.
As regards the side discussion of wound vs unwound, I make that decision dependent on the particular instrument. Unwound low G can be fine or sound thuddy (the way I pick it at least), latter case of which can be addressed by a wound string. A wound string seems to add to overtones I hear when playing the other 3 strings.
Sometimes I have two ukes strung up with low G strings. In that case I will throw on an old A string and play it reentrant until another string breaks. If I only have one uke strung with low G strings and it breaks, I will change the whole set...but only because I don't plan ahead enough to buy extra low G strings, if that is even possible with Aquila Lava low Gs.
Thus far, I've done both, but that's because I didn't like the wound G that I tried and replaced it with one that I preferred, and otherwise I'm always trying different string sets - when I change strings, I change 'em all to try something else, until I find the combination that I like. I've not yet had to replace just one string because it's worn out.
Being a classical guitarist, I truly love the sound of wound gs and have both reentrant and linear tuning on my ukes. I tend to change strings as a set although like others, have a selection of spares should need arise.
I order and change the wound 4ths separately from the rest of the set.
The wound strings in most full sets generally wear quite quickly and are neither polished nor flatwound to reduce the noise as you slide along the string. So while I may order sets with wound strings, as soon as they wear out I replace them with Fremont Soloists, which both reduce noise, wear much longer, and, to my ear, have a better tonal match. It's neither economical nor necessary to change all the strings each time. Also, string changes destabilize the tuning, and non-wound strings take significantly longer to stabilize than wound ones. I dislike playing out of tune rather more than playing with older, slightly "deader" strings.
I have six low G ukes, and some are wound, some unwound. I have come to prefer the unwound (if that matters) because there is less string noise.
But I've never felt rhe need to change just one string. So I change the whole set. I'm pretty undisciplined about whether I save a set or just discard it, but somewhere in a box, I have some fun surprises waiting.