INT 2C P - RM386 v6.00 - CLOAKING - SET SEGMENT ACCESS MODE
        AX = 0004h
        SI = selector
        CL = new access mode byte
Return: CF clear if successful
        CF set on error
            AX = error code (see AX=0000h)
SeeAlso: AX=0000h,AX=0002h,AX=0003h,AX=0005h,INT 31/AX=0009h

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