.combo2.rowsource = "" && Observe que estou limpando o RowSource da combo pra, então, alterar tmpche - o resto continua igual.

SELECT TRANSFORM(a.ingr_alu,'@L 99')+' ('+trans(c.codi_cur,'@L 999');
+'/'+TRANSFORM(a.curr_alu,'@L 99')+'-'+alltrim(c.nred_cur)+')'; 
FROM tmp_vcurso a, cursos c; 
WHERE a.curs_alu = c.codi_cur;
ORDER BY ingr_alu; 
INTO CURSOR tmpche

.combo2.rowsource = "tmpche"
.combo2.value = 1
.combo2.refresh