Gregoire,
While it may be what you are doing, I think is it extremely poor practise to erase licensed and functional versions of a product your installer did not install, especially when you do this with your trial version.
Based on your reply it is clear DxO has no intention of changing this problematic behaviour and instead force potential customers to try and find their old installer for their licensed versions if they decide your version is not worth buying. At the very least make it extremely clear in your installer that it will ‘upgrade’ (aka ERASE) any other version of the software even though that was installed by another companies installer, and make sure an acknowledgement or cancel option is provided at that time.
Jeff