A little new to C++ programming, so if I use Visual Basic to code a C++ program and add a Text label, will anyone be able to change the text in the executable with a hex editor, and if so, can I encode the text in something like Base64?
That's going to be a giant NO. The compilers and library linkers for Visual Basic and C++ are vastly different, as is the entire approach to programing. You are either programming in VB or you programming in C++. They do not mix and match.
As centauricw said, C++ and VB are completely different languages. You can't use VB to write and compile a C++ program.
That said, yes, someone with a hex editor could edit text strings in applications generated by VB or compiled with C++. Encoding the text would indeed "hide" it from prying eyes, but it would still be editable in a hex editor (as would be the entire application), so for your purposes, yes, encoding the text would "protect" it.
Well, some text in the executable will be cleartext because it's added by the compiler (mostly error message strings) and that won't tell you a lot about the program anyway. But as sea_otter points out, you just "hiding" it. Anyone with a hex editor, or really a disassembler, and some determination can crack your code, though this an advanced skill.