The Tigers will call up Nick Castellanos in the coming days if they believe that he will help the team to win games, regardless of any impact that a call up would have on his arbitration, free agency, or option status.
Once a player is called up, he begins to accrue service time for purposes of arbitration and free agency. However, that won't necessarily have an impact on Nick's calendar.
Free agency kicks in after six full seasons. 172 days counts as a season. If the time gets added so that he accrues six full seasons any sooner, then he could become a free agent one year sooner. Chances of that are pretty remote, though, because if he is optioned for less than 20 days in a season and is in the majors the rest of the time that year, he will still be credited with major league service time (and not charged with an option). So, he'd have to be sent down for more than 20, but less than 27 days (if he's called up on 9/3) all in one season in order for his call up to have an impact. Not to be cynical, but Dave Dombrowski is way too sharp to let that happen. He's all over this stuff.
Arbitration kicks in for super two status at about two years plus 140 days. So, if the 27 days or so that Castellanos would spend in the majors this season gets added to another 123 days, or just over four months, in future seasons to push him over that amount at some point, he could be eligible for arbitration a year sooner. Once again, there's a 20 day minimum period in the minors, or it will be counted as major league service time regardless.
Rookie status: A position player loses his rookie eligibility with 130 at bats or 45 days on the major league roster from April through August. However, the time on the roster in September does not count against that. If he doesn't have 50 plate appearances, he would be eligible for rookie awards next season.
Options: Nick is not currently on the 40 man roster, so he would have to be added to the roster before being called up. That means that another player would have to be removed from the roster, and put through waivers or released. If not added to the roster, he can be sent to the minors in the spring without burning an option.
Castellanos could be called up and sent down next season regardless, in which case the move now would have no impact. The only downside is if he is called up in September, sent down in the spring and isn't recalled, or is recalled and stays up all season. He then uses an option that he otherwise would not have used. The Tigers are hoping that won't matter, because he won't struggle to the point where he's up and down during three separate seasons. That would be more trouble adjusting than they'd like to see from their top prospect. He will not use an option this season whether or not he is called up.
Playoff eligibility: The Tigers could call up Castellanos by August 31st, like they did last year with Avisail Garcia, and he would then automatically be eligible for the playoff roster. If they wait another couple of days until the minor league season is finished on Labor Day, he could still be on the playoff roster if he replaces Luis Marte, Octavio Dotel, or another player who is injured at the time that playoff rosters are submitted. See Playoff Roster Eligibility Explained here.
From a development standpoint, there is little downside to bringing Castellanos up. Whether he's playing or sitting on the bench taking it all in, I see much more positive than negative. Whether he struggles or not, the experience should be beneficial. If his confidence is so fragile that struggling in the majors would be a set back, then he's got bigger issues that will eventually surface. Jordan Gorosh wrote this article about the potential impact of calling up Castellanos, and how he fits in.
The bottom line is that calling Castellanos up this season could have an impact on his contract status, but more likely it would not. The decision about whether or not to call him up will hinge on what impact he could have on the team, rather than the impact that calling him up would have on his status.