There are different ways to approach this, but none of them is standard as the Contact Form 7 Integration plugin only throws data over the line and lets CiviCRM take care of the api.
First of all, it is well possible that standard Contact Form 7 lets you specify a box that prevents submission of the data? If that is the case then that is the quickest and ...
You can create a scheduled Activity with this contact. https://docs.civicrm.org/user/en/latest/organising-your-data/activities/
via the Actions button on the contacts Summary screen
If you add the dashlet for activities to your dashboard, you will also be reminded of this whenever you log in until you mark the activity as completed.
You can connect to USPS Web Tools which will do this standardization. Go to administer > localization > address settings. Signup https://www.usps.com/business/web-tools-apis/welcome.htm and you can get it working right away. That will take care of when create / update happen.
For existing records you can use Cividesk Normalize and it allows you to perform ...
I don't think that is possible out of the box, but it would be an easy extension to write. You could use hook_civicrm_pre, look for edit/create operations on Addresses and change the relevant fields to uppercase.
Given that it's a 403 error, I would check to see if WordFence (or similar "security" plugin for WordPress) is the cause by temporarily disabling it (ideally on a test site). If you're using Apache, it may be a rogue .htaccess file causing the problem.
I began to import the database in pieces to a new installation to see if I could pinpoint where the issue might be coming up in the database. I found that the problem was with the civicm_setting table. There was a row added for address formatting that had the weird characters in it. I deleted the row and the problem disappeared.