Yes, you can manually update the name outside the applied Naming Convention parameters in Ads Manager.

Yes. In Rule Engine, for paid rules, when any naming convention rule will be defined and applied, then the rule engine will update the name as per the naming convention and no other update/edit will be required in such a case.

Yes. Once a Naming Convention is applied, it will automatically be updated if you make any changes to dependent fields (custom fields, channel fields, etc.). However, changes made in the native platform will not auto-update the name.

Custom Properties in Naming Conventions are used to make the name more relevant to the client and give more information compared to the information that can be provided by Targeting/Ad Structure alone. For example, Brand, Campaign Goal, Audience Strategy, Products advertised, etc. They also ensure that the possible values for elements of a name are defined and limited, preventing spelling errors etc.

Generally, you want information from one level to be carried down to another. So if Custom Fields are applied at the Campaign level, you may also want to use them at the Ad Set or Ad Variant level. Similarly, you may need the Ad Set level Audience fields to be used at the Ad Variant level.
It is much easier to use the Naming Convention to carry the fields down than having to extend the same field to cover multiple assets and set up tedious rules to copy tags, or even copy them by hand.

No. You will need to reapply the Naming Convention using a Macro for all campaigns to use the new one.

Yes. The new Ad Set/Ad Variant created via the Auto Boost Rule will have the Naming Convention applied. If you have selected a Naming Convention in the rule action, the Ads Manager Naming Convention will override the rule action.

Refer to the table below to understand the consequences of making any changes on the native platform.