How do I override rules defined in the base rules (Makerules.mk)?

This is done by first clearing the standard rule using the .CLEAR atom, then writing your own. Rewriting the rule without clearing it would result in the new prerequisites and/or attributes being appended to the existing standard rule.

For example to write your own rule for creating a SHARED object you would do the following:

 
    .SHARED.o : .CLEAR .USE (CC)
	    $(CC) $(CC.SHARED) $(CCLDFLAGS:N=-ptr*) -o $(<) $(*$(**):N!=*$(CC.SUFFIX.ARCHIVE))