Once you start using Adsense, they detect that you haveve placed the ad code on the specific page you sent when signing up, they will

automatically review your entire site (not just the page that you submitted in your application)

From my personal experience It doesn't matter if you change some of your website content while you are awaiting for the review process, the content of many websites changes everytime and Adsense is aware of that.

If your new content doesn't comply with any of the Adsense policy they will send you an email telling you the problem they have found expecting you to fix it as soon as possible.

Once you start using Adsense, they detect that you have placed the ad code on the specific page you sent when signing up, they will

automatically review your entire site (not just the page that you submitted in your application)

From my personal experience It doesn't matter if you change some of your website content while you are awaiting for the review process, the content of many websites changes everytime and Adsense is aware of that.

If your new content doesn't comply with any of the Adsense policy they will send you an email telling you the problem they have found expecting you to fix it as soon as possible.