Yes, you can use those stats. You can use any stats you want. But when they're so far off the stats of the official CR 1 monsters (triple the hit points, for starters!), it seems pretty unfair to pit that against four 1st-level characters.
I guess I just don't understand why they created a chart that requires so much averaging and shifting to create monsters similar to the official ones. Why not calibrate the chart to the creatures they already made and use them as a starting point?
I think it comes down to what would be the most interesting in a fight. There really isn't anything unfair about sending a CR 1 "by the chart" creature. The 4 person team will most likely tear the CR 1 creature apart. It will hit 1 of the 4 guys less than half the time (more likely 33% of the time)
A quick playtest with a level 1 Fighter, Cleric, Rogue, and Wizard
HP 80, AC 13, 2 attacks at 1d8 + 1 Avg 11, AB 3
Initiative: Fighter, Creature, Wizard, Rogue, Cleric
Round 1: Fighter hit for 10, Creature hits Fighter 1 time for 5 , Wizard uses magic missile for 12, Rogue hits once for 11, Cleric uses Healing Word to heal Fighter for 4 and hits for 8
Creature 39 hp. Fighter 11 hp Everyone else at full.
Round 2: Fighter miss, Creature misses twice, Wizard crit ray of frost for 6, Rogue hits twice for 12, Cleric hits for 5
Creature 16 hp, Fighter 11 hp, Everyone else at full
Round 3: Fighter miss, Creature hits rogue once for 3, Wizard uses ray of frost for 8, Rogue hits twice for 11 and creature is down
The party ended up with 4 damage and 2 used spell slots. I know the dice could have gone a different way, but this seems like a Medium encounter to me.
The MM creatures have special abilities that modify their difficulty. The easiest way to balance that difficulty back out is to pull back some on the HP. My guess is that is why the MM monsters have hp less than suggested.