Currently going down to one income as my partner and I are having a baby, for cashflow I thought I would change my fixed rate loan on an investment property to IO. The only reason it was P&I in the first place was I forgot to tick a box for IO previously. I always thought banks were easy to make a small change, but ING were really nasty! To change the loan, they want a new valuation fee and a switch fee.
Your loan is fixed, so that would make things more difficult. Not sure why they want a new valuation.
fixed means fixed. You can break the fixed rate, but that costs money, and if you do you will then essentially have to apply for a new loan, either with ING or a new lender. The break costs are tax deductible, it may be worthwhile investigating breaking the fixed rate, changing to IO, topping up the loan to pay fixed interest in advance. You can then bring forward a larger tax deduction while you are both working, and have better cash flow while you are down to one income. Obviously take specific tax advice from your accountant.