Oh no, if you have the size, it's no problem at all. The computer memory is just raw bytes - the computer itself doesn't care about the type. The compiler only does to simplify things for YOU, the programmer.
You can allocate a certain number of bytes with type char, then use things such as memcpy to copy over the contents of the old memory.
I can't say exactly how because I don't understand exactly what you're trying to do.