As far as I know the best way to do that in SimaPro is by copying the process you want to modify, you will then be able to change the input of electricity to what better suits your study. For better indication on how to use SimaPro, please contact their support directly.
You can learn more about the electricity sector in ecoinvent by consulting version 3.4 and 3.5 report of changes, as well as the following FAQs: How are electricity market mixes modelled? & How can I see the technology mix of an electricity market?.
Lucia Valsasina, Data analyst, ecoinvent