set_false_path -from {ModA:ModA_inst|reg_src[144..244]} -to {ModB:ModB_inst|*} ?

Tcl will not interpret stuff inside {} ... try

set_false_path -from CommandRegisters:CommandRegisters_inst|reg_command_bits -to {MetaDataGenerator:MetaDataGenerator_inst|*}

and if that does not work

set_false_path -from "CommandRegisters:CommandRegisters_inst|reg_command_bits" -to {MetaDataGenerator:MetaDataGenerator_inst|*}

Tcl treats things inside {} as a list, except when it doesn't, eg., ${i} demarks the variable and is typically used in the case where it is ambiguous, eg. $ihatetcl is ambiguous, so it needs to be ${i}hatetcl.

Tcl also treats [] as a request to execute a procedure, so in the string version above, you may need to use \[ and \] to stop Tcl interpreting the brackets.

Cheers,

Dave