Nail varnish remover often contains a solvent (acetone) which will dissolve the putty. I would be wary of using it on your dried filler. It is useful as a method of avoiding sanding filler in small gaps. You can apply the putty/filler and then remove the excess, smoothing that left in the gap, with a cotton bud moistened with the nail varnish remover. If you get it right you won't need to sand at all.Almost all model putties shrink as they dry, so more than one application may be needed.
I often use a filler made from CA glue (superglue) and talcum powder as a filler. This does not shrink BUT, and it's a big but, you must sand it before it hardens and cures, usually within a minute or two of application. If you don't it will dry harder than the surrounding plastic which can be a bit tricky. The advantage is that it won't shrink and is also an adhesive, unlike model putty.
On bigger gaps an epoxy filler like Milliput might be needed.
On really gaping gaps, like this on a PCM Spitfire:
I will insert some plastic and cut and sand it to shape like this:
Before applying a bit of putty and doing some final finishing with fine wet 'n' dry:
On the finished model:
There are lots of techniques and you'll have to find out which work best for you. I am not a big fan of model putties, except for small gaps and to smooth out relatively small imperfections.
Cheers
Steve