I don't understand why your IP feels that by remortgaging to a better rate that this will eat into your equity. Ask them to explain this to you more fully, as I assume that you are simply remortgaging the amount you currently owe to get a better repayment rate. Also, if your IP has agreed modifications on your behalf, without seeking your prior approval, this makes them null and void - but with the affect that your IVA is probably null and void as well.
The property modification you refer to is fairly normal these days, but should have been explained to you so you could consider the implications.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk