To copy the entire template store, use the COPY procedure. To copy individual templates, use the TEMPLATE procedure. There are a couple of ways to do this.
ods path work.templ(update) sashelp.tmplmst(read);
proc template;
edit styles.default;
end;
run;
proc template;
define style styles.test / store=work.templ;
parent=styles.default;
end;
run;
proc template;
link styles.test to styles.default / store=work.templ;
quit;
See also the full PROC TEMPLATE FAQ and Concepts.