There was no need for astronauts to adjust the laces. Laces were for sizing parts of the suit, not for putting them on or taking them off.
Unpressurized, the Mark IV was considered comfortable, and the plethora of straps and laces could be overcome by custom-fitting the suits to each astronaut.
Dressing for Altitude: U.S. Aviation Pressure Suits -— Wiley Post to Space Shuttle, p. 235
However, there was not time to custom-fit the Mercury suits, so the laces stayed:
By March 1960, NASA had ordered
21 modified Mark IV suits for use on
Project Mercury. NASA designated them
XN-1 through XN-4 models, but engineers
generally referred to them as “quick fix”
ibid, p. 235
The gloves were designed to be able to be removed:
The gloves used neoprene-coated fabric and
coated Helenca fabric in stretch areas along
with leather palms. A restraining wire bent to
fit the hand prevented the palm of the glove
from ballooning under pressure. The gloves
were available in 15 sizes, consisting of 5 palm
sizes with short, regular, or long fingers. The
gloves attached using sealed disconnects
secured by a slide-fastener zipper.
ibid, p. 228
Schirra and Gordon had longer Mercury flights, and each ate during their flight, though it is unclear if they removed their gloves.
All suits starting with Gemini were designed with wrist disconnects that allow an astronaut to don and doff their own gloves.