How to enable block inside fifty different sections without copying meta code?

I am developing a Shopify Theme. The structure I have now is (excerpt):

Snippets

custom-message-snippet

Sections
custom-message-section

welcome-page-a-section
welcome-page-b-section

Templates
welcome-page-a-template
welcome-page-b-template

Custom message snippet uses settings that are in the custom-message-section, that is:

a) message
b) header text

I’d like for users to be able to add custom-message-snippet to welcome-page-a and welcome-page-b in a way that settings for both are different.

I can not render section 'custom-message-section" inside welcome pages because it is not possible (and a workaround is nasty).

There are fifty welcome pages. Every welcome page is totally different.

My question is:

How to allow users to use custom-message-snippet in all welcome pages without copying and pasting custom-message-page setting schema to each and every welcome page?