The verse says ‘thus’; implying constraint - אמר קרא ככה עיכובא
The term ככה יעשה indicates that the only action that can release a יבמה is חליצה (but not גט). However, it does not exclude that she cannot be released in other ways which do not require action, for instance מיתת היבם.
However were it not so we would utilize the ק"ו even though חוקה is written there - הא לאו הכי דרשינן קל וחומר אף על גב דכתיב ביה חוקה
We derive from the ברייתא that a ק"ו can override the עיכבוא of אשר עלה (which is stated twice [לעיכובא]). Alternately we derive it from the fact there is a necessity for the מיעוטים of זאת and ועשהו חטאת.