Frank is exactly right. If you edited files without creating a custom template, it's not too late. Install 1.3.7 in its own directory with its own database and start recreating your template. You mentioned english.php as an example. If you edited it without saving it to your own template, make a copy of it in the 1.3.7 test site for your custom template and use something like WinMerge to compare the old english.php to the new default one you just copied. You can make the same changes to the new one and save it to your new template. You can do that for each file you changed. It might be difficult, but if you're careful, you can get it done. Think of it this way... it'll make upgrading easier in future.
To create a very basic custom template (you can build from there), you need:
includes\languages\YOUR_TEMPLATE\english.php
includes\languages\english\YOUR_TEMPLATE\index.php
includes\languages\english\YOUR_TEMPLATE\header.php (to change the logo)
includes\templates\YOUR_TEMPLATE\template_info.php
includes\templates\YOUR_TEMPLATE\common\tpl_header.php
includes\templates\YOUR_TEMPLATE\images\logo.gif
includes\templates\YOUR_TEMPLATE\css\stylesheet.css
Any where you see a \classic\ folder, you can create a folder for your custom template.




