It depends on whether you're working on the main-line or not.
Earlier this week, I mistakenly converted the main-line of an app to 7.14.1 before it was tested and wanted to go back to 7.13.1. Mendix told me it wasn't possible with the platform and pointed me to a very old forum thread (3033) about TortoiseSVN. What I ended up doing, however, was the following:
- Open the project in 7.14.1
- Go to Project -> More versioning -> Manage branch lines
- Under Branch lines, click 'New'
- Create a branch from the mainline, select the last revision in 7.13.1 (the one before you converted) and click 'OK'
- Give it a name, e.g. 'Temporary-main-line-7-13-1'
- There will be a pop-up question: Do you want to download and open the branch line? Answer No!
- Open this new branch line in 7.13.1 and tell your team (with a mea culpa).
You can make new branches in 7.13.1 from this temporary main-line, e.g. a branch to test the conversion to 7.14.1. Once the team is ready to convert, you can do so and merge this branch back into the 7.14.1 main-line.
I think you misunderstand your modeler's and project's versions. Your team's project is on version 7.13. Your modeler version was 7.13.
When you decided to upgrade to 7.14, what you have done is:
- installed a second modeler, this time modeler version 7.14
- opened your team's project in your new modeler and thus UPGRADED THE PROJECT to 7.14
Now you still have version 7.13 of the modeler on your laptop.
So to answer your question on 'Is there a way to downgrade modeler version? ': No, just open version 7,13 of your modeler.
Related to this: is there a way to downgrade your project from 7.14 to 7.13? Simple answer: No.
So to answer your question on 'how to prevent the modeler aksing to locally upgrade': Start version 7.13 of your modeler and open the project's version 7.13
Can you save the changes you have made since you upgraded to 7.14? Not automatically. Only manually by opening the 7.14 version in your version 7.14 modeler and look at the changes you made. (Appstore's "Mendix DiffTool" might be helpful)
Honestly I cannot fully follow your way of working (what do you install/uninstall?)
1. You can have as many different modeler versions installed as you wish.
2. You cannot downgrade a project to a lower modeler version.
3. You can choose not to convert a project - you cannot open it in that modeler version then neither
You can always locally test upgrading a project (or create a new branch for that) but going the full upgrade path should really be planned and tested properly.