Change settings without restarting LMMS

I am posting this issue as a place to discuss whether it's possible or not to change settings without having to restart LMMS.

I believe some cases will be very difficult or impossible to implement, but maybe we can track these cases and only require restarting for those?

Start by reading the issue and its 27-comment discussion to understand which settings are being considered and whether any cases are already known to require a restart. The issue does not name files, entry points, or tests; work is not ready to start until the desired scope and completion criteria are agreed.

Written by the indexing model from the issue text.