Proc Append with Matching Variables and Variable Types
This works as desired.

proc append base=classlib.htwtdata 
		data=moredata
		    (rename=(h=height w=weight g=gender));
run;

SAS Log:

NOTE: Appending WORK.MOREDATA to CLASSLIB.HTWTDATA.
NOTE: There were 2 observations read from the data set WORK.MOREDATA.
NOTE: 2 observations added.
NOTE: The data set CLASSLIB.HTWTDATA has 6 observations and 3 variables.
NOTE: PROCEDURE APPEND used:
      real time           0.17 seconds
      cpu time            0.10 seconds