Hello, I am Keith, one of the experts on Just Answer, and happy to help you with your question.
Sorry, got it; although I live in Scotland questions on LBTT are exceedingly rare. ADS is the additional tax payable upon the purchase of second homes which would apply in your case. As you surmise you can get this back if you sell one of your residences within a given period, but you do not appear to want to do this. Remember too that one of these dwellings will be subject to Capital Gains Tax (CGT) on ultimate disposal, but you have two years after a second purchase to elect which residence you wish Private Residence Relief (PRR), which relieves at 100%, to apply. The purpose of ADS is to deter second home owner ships to free up the housing market. Here is the guidance from Revenue Scotland:
'The ADS applies to most purchases of additional dwellings by individuals in Scotland where, at the end of the day that is the effective date of the transaction, a buyer owns two or more dwellings and is not replacing their main residence. It also applies to most purchases of dwellings by non-natural persons (e.g. companies, partnerships) in Scotland.'
Should you decide to sell for the last 18 months of ownership you are deemed to be in residence even if this is not the case and PRR is extended to cover this period.
I do hope that you have found my reply of assistance.