For this kind of encryption, any operation between plaintext symbols and the random masking symbols that belongs to a commutative group can be used.
Nevertheless, modular addition, including addition modulo 2, a.k.a. XOR, is almost always chosen, because any other kind of operations are slower in hardware without having any advantages over modular addition (when the masking symbols cannot be distinguished from a random sequence).
For example, instead of using modular addition, you can use multiplication modulo 2^16+1 (a Fermat prime number), to encrypt each 16-bit plaintext symbol, but that is slower than modular addition without being better (unless your method of generating the pseudo-random mask is weak, which is easy to avoid).
