Eligibility/substitution

[ManInBlue]

FED Case Book CR2: Jones runs for F2 in the first inning, but Smith runs for F2 in the third inning.

Is this a substitution? Is Jones eligible to enter the game on defense? Can he be used again as a CR for F2?

I had never considered the first 2 parts of this question - although I lean toward "CR does not effect substitutions". I'm thinking though that Jones cannot be used as a CR any longer.

Another sitch: CR11 - F2 singles and is replaced by a courtesy runner. B2 walks. Before the next pitch, the CR is replaced by another CR. Is this a substitution? Can the original CR return in any capacity?

Any help would be appreciated.