Is there any way to disable the chat message upon joining a world of [Mekanism] Using developer build x.x?

Yes, see the config, it was renamed to v2 for users that switched to mekanisn ce and wasnt aware that we support this function. Im gonna rewrite the readme soon and i will include this.

I can also remotely deactivate it till you update the pack with the new config if needed.

Also a new version is around the corner with fixes for minetweaker and will include #36

The whitelist dim for windmills feature will be added in 9.10.17

PS: remember to turn off the voiceserver in the config, its a security risk and im not supporting it.

Wait, dev build? Uh so its not the update message?. Can you take a screenshot?

I disabled UpdateNotificationsv2 and it doesn't seem to happen anymore :)
For reference, that's how it looked like:

Ah, its because i havent updated versionnumber at remote

but ye, modpacks should have thhat setting as false regardless