Can I swap one plugin with another of the same price?

Can I swap one plugin with another of the same price?

No, you cannot swap one plugin with another of the same price. Two plugins, despite the same price, offer different complementary features and functionality. Once a plugin is deactivated all the features and functionality that were added to the application upon plugin activation are removed. However, the data pertaining to the plugin is retained till the end of your current billing cycle. At the start of the next billing cycle, this data is purged from the application, the only exception being the payment processor plugins. The plugin data for these plugins typically comprises the reference numbers and auth numbers for the credit card transactions done when the plugin was active, and that is why this data is retained for reporting purposes. 
Plugins in Tagrain are either Subscription Based or License Based. So the price that you pay for your plugins is based on the number of POS terminals that you have in your setup and the number of licences that you have acquired.
There will be no change in your subscription amount in the current billing cycle if you are only deactivating the plugin AND not updating your Store / POS count.