This step must be performed on the original project file used to create the translation sibling in Step 1. Only this file will have the correct Project GUID that can be used for synchronization in the next step.
That is all you need to know about this step. Simply work on your project normally, making any necessary changes, deletions and additions. There are no restrictions on the changes you can make.
To make the translator's work easier use the comments and bookmarks features to identify the text that has been changed. You can write comments to explain where the changes are, particularly if they are only in the – otherwise the translator may waste a lot of time trying to find changes in the text that are not there!