Is there a component so when a topic is marked as Solved, the topic gets locked and a custom message is posted with it?

[Moin]

You can auto-close solved topics

@sam

Auto-close topic once solved

From the main Solved admin settings you can set a timer to close a topic once it has received a solution using the solved topics auto close hours admin setting:

Alternatively, one can be set per category from the category wrench menu on the Settings tab: