Well, rules will certainly change in terms of unused skills getting implemented over time or minor changes being made to the weight of one particular skill or another in equations, but the skills you see now are the skills you get! Hopefully it is relatively clear what each skill does or will do, and those factors are quite unlikely to change significantly.
As Calgor Grim points out, any particularly big changes would indeed most likely result in a refunding of those skill points, but the current setup was given a whole lot of thought in terms of gameplay direction. I would go ahead and spend your skill points, unless you aren't doing anything at all in-game that would benefit from having any skills assigned. Just sit on your level-up points, perhaps, if you are worried.