According to
replace value of (XML DML) - SQL Server | Microsoft Docs[
^],
replace value of (/StoreConfigurations/Hosts/Host/StoreNumber/text())[1]
with ""
Or, you can try to delete then insert;
delete /StoreConfigurations/Hosts/Host/StoreNumber
insert <StoreNumber /> as last into (/StoreConfigurations/Hosts/Host)[1]
if you really want the self-closing tag.