What is the likelihood of HRC approving a reclassification for someone re-enlisting for the first time?

As an initial term soldier you usually have the option to reclassify it may not be to that particular MOS as I do not know the In/Out call on that one or eligibility requirements so that would be the first step, make sure you are qualified to go into the one you want. Beyond that I don’t see why it would be difficult

Depends on whether or not you are in an over strength or under strength MOS and what the in and out Call is. Your re-enlistment NCO will know what they are.

Strictly depends on the strengths of the MOS. HRC will analyze the strengths. Anyone else who says it's likely or isn't, is just making wild assumptions.