do the new thing inside @combine

(upstream already does the protect and incsname for us)

unicodedomino.sty

@@ -90,7 +90,7 @@
  }%
 \else%
  % v1.2i 2019/07/09, or newer
- \long\def\UTFviii@two@octets#1#2{%
+ \long\def\UTFviii@two@octets@combine#1#2{%
   \ifx\protect\@typeset@protect%
    \edef\unicodedomino@tmp{#1\unicodedomino@last{\string#2}}%
    \expandafter\unicodedomino@octets\unicodedomino@tmp\empty%
@@ -99,7 +99,7 @@
    \string#1\string#2%
   \fi%
  }%
- \long\def\UTFviii@three@octets#1#2#3{%
+ \long\def\UTFviii@three@octets@combine#1#2#3{%
   \ifx\protect\@typeset@protect%
    \edef\unicodedomino@tmp{#1\unicodedomino@last{\string#2}\unicodedomino@last{\string#3}}%
    \expandafter\unicodedomino@octets\unicodedomino@tmp\empty%
@@ -108,7 +108,7 @@
    \string#1\string#2\string#3%
   \fi%
  }%
- \long\def\UTFviii@four@octets#1#2#3#4{%
+ \long\def\UTFviii@four@octets@combine#1#2#3#4{%
   \ifx\protect\@typeset@protect%
    \edef\unicodedomino@tmp{#1\unicodedomino@last{\string#2}\unicodedomino@last{\string#3}\unicodedomino@last{\string#4}}%
    \expandafter\unicodedomino@octets\unicodedomino@tmp\empty%