Everything can be hack... when I build protections, I try to make it more costly to hack then the value of what I try to protect...
I don't want to be negative but... what you described is child's play to break, an exercise for newbies, hacking 0.001, the kid will graduate to a chocolate ice cream.
You'll spend a lot more time encoding and decoding and, who knows what else, than someone who knows what he's doing is going to spend breaking it.
Big companies, Adobe and Autodesk among others have protection mechanisms that are really difficult to break and they are routinely broken. As I stated in the previous sentence, you'll spend more time building the protection than the hacker is going to spend breaking it. Save your time.
If you don't want them to be readable in a hex file viewer, just use a simple xor algorithm like Thaddy suggested. The point isn't to "protect" the strings, only to make them unreadable with the most trivial of tools.
For the record, it isn't my intention to criticize.