As Merlin says, this "saving" will be added to your disposable income and, therefore, to your IVA payment. If you can get a F&F through, based on the current payment, it will work out a lot less expensive ... but .. there is always a "but" .... CF are currently at odds with creditors over their paperwork and variations such as this are currently on hold ... nobody knows for how long!
Another way of looking at this, if you do get to have to increase your IVA payment ....... you will be no better off, yes, but, you will be no worse off.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk