Answer from cs61c-ep (Hao Wen Vivian Chong 15826235) for Question 1
No, they cannot. If they did, one would have to implement a way for the assembler to tell which instruction is being called. They eliminated this possibility by having different bits in the opcode to tell which type of instruction it is. So, if two MIPS instructions have the same bit pattern, they will be the same instruction.