Can the president appoint/ hire federal aganets?

I was looking up what all the federal marshals do and I read where the president can appoint a district us marshal (the top dog not deputy marshels) so it made me wonder can he do the same for say homeland security agents or ncis agents? Also it said us marshels are a little hearder to get on because they dont require a bachlers degree....so can people with ged/high school diplomas be an agent or would you need at least some college or military exsperince? Also wondering if marshals have  jurisdiction outside the United States? and where I read Homeland Security agents have jurisdiction outside of the United States they did not say what all they can do, are they like the FBI and have to have help from law enforcement of that country that they are in or can I go after somebody on their own? Like NCIS, atf and cia agents can do. With president sending in federal agents to cities like Chicago I wonder if ncis is helping? The news said FBI,ATF,DEA,DHS and us marshals are defently the main agents on this new taskforce. ....also let just say i think its sad that it took the mother of a kid shot in Chicago asking the president for help since the mayer told her theres nothin that could be done to get our government to clean up crime.....where was this 4 years ago or even 8....or after 2001?