The sandbox I am working on now had distinct system admin profile settings, after deploying a changeset from another vendor our system admin profile configuration was overwritten and we can not access the org anymore using our user for some reason. Is there any way to revert changeset effects from the System admin profile or retrieve the previous version for the system admin profile?
Is there any way to revert change set effects from System admin profile or retrieve the previous version for system admin profile?
No. Salesforce does not have an inherent versioning system for metadata. If you have an existing sandbox that has not been refreshed, you may be able to re-deploy the old settings from there if you can identify what specific components were changed, but change sets won't just deploy a whole Profile.
This is an important reason to use source control as your source of truth. If you're not comfortable setting up and using version control, many vendors are happy to sell you dev ops/lifecycle management tools for Salesforce.