How can I update a redis value without affecting the remaining TTL?

The KEEPTTL option will be added to SET in redis>=6.0

https://redis.io/commands/set

https://github.com/antirez/redis/pull/6679

The SET command supports a set of options that modify its behavior:

EX seconds -- Set the specified expire time, in seconds.
PX milliseconds -- Set the specified expire time, in milliseconds.
NX -- Only set the key if it does not already exist.
XX -- Only set the key if it already exist.
(!) KEEPTTL -- Retain the time to live associated with the key.