Can I replace the black toner with white toner, without owning a white toner printer?

Unfortunately, no. It is not that simple. Apart from needing white toner, your OKI printer also has to know where to print white. Theoretically, if you could place a white toner instead of the black toner, the printer will just print white where it used to print black and that is not what you want. In reality the printer will recognize the white toner as a “wrong” cartridge and it will generate an error preventing you to make the mistake of placing a white toner in a CMYK OKI printer.