Feature Request: Newsletter Block - Customize wording for Free subscription when Paid Newsletter Tier is present

### Impacted plugin

Jetpack

### What

Allow for customization of the sentence "Get a glimpse of the newsletter" which appears in the Newsletter Subscription popup when a site has a Paid Newsletter Tier active.

### How

When a site has a Paid Newsletter active, visitors that want to subscribe to the site can choose from the paid _and_ free version of the newsletter.

In the screenshot below, the Newsletter Tier has an option to subscribe for $1 per month. The Free version is also available. This description can be customized by the site owner since the "Newsletter Tier" is replaced with the name of the subscription.

The description for the Free version is: "**Get a glimpse of the newsletter**".
This description _can not_ be personalized.

We would like the text to read: "**Subscribe to My Blog For Free**"
or to be customizable by the site owner.

The content of the "membership-modal-window" is in an iframe so it can't be customized with a plugin like CodeSnippets.

Is there a way to customize that text?

(9277242-zen)

The issue identifies the newsletter subscription popup and its “Get a glimpse of the newsletter” wording, but names no source files, tests, or implementation entry point. Start by searching the Jetpack codebase for that text and tracing where the membership modal's free option is rendered. Done means the site owner can customize the wording, or the requested text is used, when a paid newsletter tier is present.

Written by the indexing model from the issue text.