Fly lines meant for cold weather will work fine in warm weather. The reverse is not the case.
Why I've asked for suggestion on lines for Nilo's 4wt...
I've had my trout lines, that worked perfectly on Colorado, and Pennsylvania, feel gummy and limp here on our local ponds.
And I've had lines that I use for redfish coil up into an uncontrollable mess when fishing for sheephead in the winter.