What I do is break the song down into parts..
So in a song with 50 chords, I break , say a sentence or 2/ a verse down into an independent progression..which is normally between 3-6 chords.
I play that part as many times as necessary for it to register in my mind & hands..(this is where having a good chord vocab. is advantageous because you don't have to do it so many times..).
if the song is too long, I play maybe a set of 3 progressions I've segmented to assess if it has actually registered in my head..(ie, in a 50 chord song it means I've played 3 sets *4 chords= 12 chords, now I know I have this part for good for the next few days
, unless if I ignore the song completely after learning it)
So the trick for me is to play mini parts of the song & then add them together..
Remember also, that most songs repeat their progressions, so what might seem like a 5o chords galore, might actually be 13 chords, maybe with 1 or 2 chord changes later on in a progression you've already grasped.
I hope this makes sense & is handy.