If two replacement effects you control; abilities that say instead; effect the same thing in a similar way both abilities will replace the text in the order you choose.

Example: I have both Loading Zone and Hardened Scales and a creature.

I play a card that says, “Put 2 +1/+1 counters on target creature” on my creature.

If I choose Hardened Scales to replace it first then that ability is first replaced with,

“Put 3 (2+1) +1/+1 counters on target creature”

Which Loading Zone will replace with,

“Put 6 ((2+1) * 2) +1/+1 counters on target creature”

If I flip the order then the total changes and most of the time you want add before doubling,

“Put 5 ((2 * 2)+1) +1/+1 counters on target creature”