Can I manually invert source and target languages in an XLF?

A German customer of ours sends us .xlf files so we can translate training units into English for them. The xlf files are exported from some learning management system (possibly Ilias).

The source language of the xlf is German and the target language is English.

The customer also needs Spanish translations, but they have always used my English translation as the source language for their Spanish translations. Currently, they import my English translation into their software, create a new training unit in English then generate a new .xlf file with English as the source language and Spanish as the target. However, they want to cut out this process, if possible.

Is there an easy way to manually invert the German-to-English .xlf file so that English becomes the source language and German the target language?

If we could do that, it would then be simple to manually rename the target language in the .xlf as Spanish (using notepad++). When the Spanish translator then opens the .xlf in Trados Studio they will then see English in the source column and German in the target column, but can simply clear all target segments before they start translating the English.

I've scoured the forums, but can't seem to find a solution.

Thanks in advance,

Andrew