Unfortunately no, you cannot do this.
You are looking for some kind of goto and this is difficult to implement.
However, we have started to implement some (limited) "break" feature, and maybe this could be useful for you:
Example:
@startuml
start
repeat
:Test something;
if (Something went wrong?) then (no)
:OK;
break
endif
->NOK;
:Alert "Error with long text";
repeat while (Something went wrong with long text?) is (yes)
->no;
:Alert "Sucess";
stop
@enduml