Should i be able to change

--logger_tls_max_lines

using FleetDM? According to osquery help it seems that i should be able to, but the change does not take effect and it seems to let the osquery in a weird status where it stats using a lot of memory but does not output any logs.

In theory, yes. In practice we have seen that some osquery options that should be configurable after startup have bugs that prevent that. If you find that, please file a bug on the osquery repo.

ok, i will do that