The Workflow will use two different cover page templates for the "electronic signature" function (each model contains a title, author, date etc ). The chosen template will depend on the type of object initiated in the WF (AEDE_Commerciale or AEDE_Specifique) then there will be a PDF generation signed with one of the templates depending on the initiate object.
The kind of automation you describe would probably require ITK to create a custom handler. However, if you flip the logic, you can likely do this by leveraging workflow filtering.
For instance, config workflow filter for AEDE_Commerciale to use WF1 and config workflow filtering for AEDE_Specifique to use WF2. When AEDE_Commeriale is sent to workflow then only WF1 is listed and you can use the appropriate signed template. When AEDE_Specifique is sent to workflow then only WF2 is available and then you use that signed template.
The limitation is that you cannot send both AEDE_Commerciale and AEDE_Specifique through the same workflow and have divergent paths. For that you need code. Although you might be able to do something with sub-workflows where AEDE_Commerciale launches WF1 and AEDE_Specifique launches WF2 but it starts to get pretty complicated.
My advice, keep it simple. Don't make one workflow try to cover multiple business cases. One workflow per business case is ideal.