You could write:
This autistic dance group has made history at the European championships. Now they want to change the way we all see young people with autism.
This hasn't altered the meaning of the sentence. By combining the two sentences into one sentence with your conjunction, the comma can be seen as politeness to your reader, as expecting them to read:
This autistic dance group has made history at the European championships and now they want to change the way we all see young people with autism.
can be seen as a bit of a challenge!