Core files modified, what next?

Question

My developer with questionable code practices modified a few core files, We tried to integrate a new theme and a few blocks are posing a problem.

The site has been running for over 6 months and I don't want to waste all the SEO efforts.

My development team is suggesting 3 options

1. New instance of magento altogether
2. Custom theme developemnt
3. Upgrading magento version from 1.9.1 to 1.9.3

Answer 1

Before doing anything I suggest you create a dev site, like dev.example.com and clone the live website there, so the sales continue on the live website.

For the issue you're having, I suggest the following steps:

1. Copy app/code/core to another directory outside the web directory (site_core for example).
2. Download Magento 1.9.1 and copy it's app/code/core to another directory named core_original
3. Compare the two directories with rsync:
   rsync --dry-run -vz -rlD --ignore-times --no-perms core_original/ site_core > results.txt
   You MUST use --dry-run if you want to see the changes only and not push the changes from core_original to site_core. Check results.txt file for the changed files. If the command didn't work properly, check rsync command options here: https://linux.die.net/man/1/rsync
4. Override those core files properly in app/code/local/Mage.
5. Confirm everything is working properly as before.
6. Update Magento to the latest version if you prefer (although I would suggest so for performance and security reasons).
7. Re-test the website if the overrides are working properly (if you don't need them, remove them).
8. Update the theme and modules if you don't have the latest version.
9. Fully test everything on the website.
10. Deploy the changes to the live site (but before do a backup of the files and database, and put the store into maintenance).