Changing to a 50T chainring will probably need the derailleur to be lowered, in which case you will pretty much need to reset it completely (alignment, limit screws and cable tension as well). Depending on the age and type of derailleur, it may not even be compatible with smaller chainrings. But it is usually best practise to see if it will work corectly with your curent FD first.
In my experience FDs are usually mounted far to high to offer optimal performance anyway. Manufacturers usually specify that the cage must be 0.5 to 2mm above the tips of the teeth on the big ring. I usually shoot for about 1mm clearance.
There's a pretty easy way to check for the chain being too tight. The whole question for chain length - long or short - is: will the normal front to back swing of the rear derailleur be adequate for both the "big big" and "small small" combinations. When it rotates backwards for the small-small, does the chain actually double back on itself (chain too long). When it rotates forwards for the big-big, does the chain pull it completely forward, or is there still some give in it.
Shift onto the big ring in front, then shift up to the big sprocket in back (carefully, slowly if you're unsure) so you're on the "big big" combo. Look at how it tracks through the rear derailleur. The RD will be very much angled forward on this combo, which is what it is supposed to do. But, if the chain actually curves around the RD wheels rather than making a virtually straight line, and the RD still has a little movement available, it is long enough.
hi test rode it already, everything is fine, i also made the suggested big-big and small-small test,
i also reinforced my reason to buy them, since there are long discussions about compact versus standard cranksets,
all's well that ends well !