I know, and know of, many prominent artists who regularly fill the pans with paint from the tubes, andy they have had no problem with the quality or problems with the breaking down of the binders. There are various types of binders and one of the most popular is gum arabic. The tube paints normally have a little bit more binder in them than the paint in pans, and as such make them easier to mix. All the components are the same - just in different proportions.
So I ask the question - why would rewetting them cause the binder to break down in the first place, and secondly, why would the binder break down when actually there is more binder in them than the pans? All the components are the same and when the tube paints dry in the pans they are just the same as the pan paint, only with a bit more binder.
Some manufacturers even add a touch of honey (an anhydrous substance) to the paint to keep them slightly moist.
As can be seen in one of my previous posts I used tube paints squeezed into pans. To keep them moist longer I use plastic pill/capsule holders with lids. I just add a drop of water every so often and then close the lids. Even before using these holder I have never ever had any quality problems with my watercolour paintings.
