Modify parameter for memory instance

I use Synplify Premier for Synthesis and Quartus II v11.1 for place and route. The design uses synthesis directive to infer RAM. When I use the netlist (VQM) for place and route, I get the following critical warning:

Critical Warning (15003):  "mixed_port_feed_through_mode" parameter of RAM atom top|sub_module|m_0__ram_block1a_0 cannot have value "old" when different read and write clocks are used.

I understood that the parameter must be set to "don't care". So I tried to use TCL script to modify the parameter assignment.

set_parameter -name MIXED_PORT_FEED_THROUGH_MODE DONT_CARE -to "top|sub_module|m_0__ram_block1a_0"

I verified through Assignment Editor that the assignment had been taken but still I get the same critical warning. Am I doing something wrong :confused:?