How to instruct sed to substitute only once while using multiple substitute expressions?

Use the t command after each s command to branch to the end of the script if a substitution was made:

sed -e 's/something/else/;t' \
    -e 's/one/two/;t' \
    -e 's/two/three/;t' <<<"one"

Here, the t command after the last substitution is not needed, but if you generate this code automatically, there is no problem letting it suffix each s, even the last.

sed with branch 't' in other command is the perfect answer.

This is just a suggestion , in case if you want to do multiple stuff inside if its replaced , you can use awk:

awk ' { if (gsub("something","else",$0) || gsub("one","two",$0) || gsub("two","three",$0) ){ print $0;exit}; }' <<<"one"