>

The latter phenomenon has been playing out in the United States to an extent. 
Racial minorities moving into suburban communities has helped shift the white populations in those suburbs towards more socially progressive attitudes.
It doesn't seem very likely.  Ethnic diversity is not enough for genocide.  You also have to have serious economic amd political issues.  It's more likely that in the generation or two required for that level of immigration, immigrants acquire significant financial and political influence. >

Tbh reading your post makes you seem like a far right "great replacement" nut job...
It would entirely depend on how the governments of these countries are dealing with the refugees. If the immigrate then stagnate in low income/subsidised work for years, being isolated in migrant neighbourhoods and communities, then maybe. Low income means now power or influence, isolation means no real presence, easy for you to be made a scapegoat. 
If the Govts are integrating these people into the workforce and community, allowing them and their children real access to education. If the people are welcomed into local community councils, groups, sports clubs etc, and people get face to face exposure. Then it makes it hard to other someone you have a connection with.
Normalising ethic practices and habits helps too. If Ahmed has to go pray 4 times a day and nobody knows what it's about, OG folk are going to bitch about it in their cirgarette breaks. Etc