The country you choose when signing up for a new account is permanent and cannot be changed once the account is established. The country chosen will determine which currency your monthly subscription will be charged in, and also the name of the tax type used for your invoices should you choose to use the tax calculator, for example VAT in the UK. A workaround for the incorrect tax ID name for your region is to not activate the tax calculator in the Cavanti system, then simply setup all applicable invoice items to be priced tax inclusive, and perhaps mention the amount and type of tax charged in the item description if more detail is required. You can toggle the tax engine on or off in the web app under settings>other settings>tax>do you charge tax?
All other instances of your address throughout the app can be changed. For example the address shown on all outward documents such as invoices and session reports can be customized on the web app under settings>other settings>letterhead, and your email signature can be edited from settings>user preferences.