For example, in the mtcars dataset, how do I rename the row Merc 280 and call it Some Mercedes?
All other posts seem to answer how to replace all row names at once.
You could subset the rownames of mtcars and then update
df <- mtcars
rownames(df)[rownames(df) == "Merc 280"] <- "Some Mercedes"
df
# mpg cyl disp hp drat wt qsec vs am gear carb
#Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
#Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
#Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
#Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
#Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
#Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
#Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
#Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
#Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
#Some Mercedes 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
#Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
#.....