I'd sent a replacement as a substitute (7)
I believe the answer is:
instead
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">as a substitute</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">i'd sent a replacement</span>' is the wordplay.<br/ >'<span class="explanation-format__original">replacement</span>' is an anagram indicator.<br/ >'<span class="explanation-format__original">id</span>'+'<span class="explanation-format__original">sent</span>'+'<span class="explanation-format__original">a</span>'='<span class="explanation-format__intermediate">idsenta</span>'<br/ >'<span class="explanation-format__intermediate">idsenta</span>' is an anagram of '<span class="explanation-format__answer">INSTEAD</span>'.<br/ ></span>
(Other definitions for instead that I've seen before include "In lieu" , "for a change" , "as an alternative option" , "As a substitute" , "Rather - detains (anag)" .)