Not a good idea, don't even think of it! Well you may, considering all the consequences. Here I'll tell you where the counter values are stored in the database.
Table dbo.OrganizationBase as shown on your left which is stored under OrgName_MSCRM Database.
Take a sneak peek at the table content and you can notice the prefixes and counter value of KB article, Case and Contract entities. Now you can manipulate, AT YOUR OWN RISK!