Changing UID and GID with SSH

In order to run a certain docker application (JetBrains YouTrack) I need to make modifications to a dedicated user and user group I created.

I know that the UID and GID cannot be changed within the DSM UI and that numbers below a certain value are not allowed. I'm also fine if both the user and the group will not show up in the UI as theses are only used for that one and only purpose.

So, how can I change both the UID and GID of a user and a group not used anywhere else to a value of 13001?

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Thanks!