I've read that just because a player is listed as a CF does not mean he should play there.

Is it my choice to play a player at any position of my choosing?  For example, can I have a CF play 1B?

if I do so, will I hurt his defensive range/glove ratings after one season at 1B?  

Or there is no difference in that the player will progress/regress defensively anyways.

I'm asking because I need a starting 1B at the ML but don't have a serviceable one.  I either have to sign a FA 1B or promote from AAA.  The thing is I have a CF in AAA that's a comparable hitter with any FA 1B that I can afford.  I might as well promote that AAA CF to play 1B for much cheaper than signing a FA.

it won't hurt a player's ratings to play him out of position, ( i think it will only hurt if the player is not develped yet, you want tp play your SS, CF at those positions in the minors when possible)  playing a CF ( 80's in range  and glove minimum for CF) will result in a gold glove 1B and it won't hurt his rating. ratings don't go down because they play out of position. if you look at the recomendation for each position they are pretty much the minimum you need i always try to be well above the minimums if possible.  something that will help is check out the better teams and look at where they play their players and what kind of ratings they have , also check out previos award winners and see what ratings get you gold glove caliber play at which position

"The thing is I have a CF in AAA that's a comparable hitter with any FA 1B I can afford."

A few possibilities here:

(1) There are no good 1B FA's. This could be the truth. However, remember that, since you can play anybody anywhere (just making sure their defense is good enough), don't just look for FA 1B to fill your lineup out. Look at LFs and RFs, 3Bs, even DHs, etc. Search for the hitting ratings you want first, then see what their defense ratings are and if they are acceptable to you.

(2) There are good FAs but they are too expensive for you. Pick a whole bunch of guys and add them to your list of free agent targets. Keep tabs on them as the FA process goes on. Many of them will wind up dropping their demands if no team is willing to offer them. Often, you can get a decent-but-not-great aging 1B on a 1 or 2-year deal for 2-3M after the top-tier guys have been signed.

(3) Your CF is a legit stud. A legit CF (with Range and Glove both over 80) who can hit like a 1B is a potential MVP candidate. Definitely promote him. However, don't just plug him into 1B. If he's defensively your best CF, put him in CF. If not, put him at 2B, just make sure he's not left-handed. If he is left-handed, and slightly worse than your current CF, but your current CF is right-handed, then put him at CF and slide your current CF to 2B, your current 2B to 3B or LF (depending on his arm) and your current 3B/LF to 1B.

I would never play a legit CF in 1B though. I would much rather have him at 2B (if RH) or LF (if LH).

You can change a player's primary defensive position by clicking on the hyperlink embedded in the position (i.e. 1b) on the GM Office->Roster Management screen. 

IMO, the "recs" that SIMMY pre-fills (when you click on "Show Recs (Proj)" are always a bit optimistic. Specifically, SIMMY seems to have different "minimums" (especially at the major league level) than I do. SIMMY will often say that a guy with 70+ range and 70+ glove is a 2b; I find that those ratings produce a below average major league 2b. SIMMY will also allow anyone with 3 of the 4 needed SS ratings to be coded a "SS", even if one of the ratings is well-below average (ex. 60-ish range or glove)

To get close to "Gold Glove" quality, the ratings generally need to be +5 on the recs. I've seen lots of times that's not true, so don't bother arguing about it - but the point is that IMO, to have the best chance at "Gold Glove" defense at any position, the guy has to have ratings that are higher than the SIMMY recommendations, often in more than one category. (For example, a 100-100-100-100 player has a much, much better chance of being GG-quality at SS than a 80-80-80-80 guy.)
 

I don't know that I'd bring up Dillon, assuming that is the guy you're talking about.  I like my middle of the field guys to develop defensively before bringing them up.  Being he's a two year pro still, he'll have some room to grow.

I'm not able to look at all free agents, but looking through some who Left via FA according to League Tranactions, Gene Caufield is a FA and put up an .852 OPS last season.  He's switch hitter with a good eye and good power, and would be a cheap, fill-in type guy.  Or Hick Carter could be a quality guy in a platoon role, if you can find a partner for him.  He's listed as a LF, so you might want to expand your parameters in a FA search.  Pretty much anyone can play 1B in my opinion.

thanks to all who chimed in.