Depending on what sight you have on the gun, installing a different sight will probably require re-sighting the gun.
If you're replacing the same type of genuine Colt sight, only with an insert, it'll probably need no changes.
Installing a genuine Colt Python sight should pose no problems.
You'll need a small "starter" punch, a standard length punch, a small hammer, and some wood blocks to support the barrel.
The "starter" punch is simply a standard punch cut off to about 1/2" inch working length.
This prevents the punch from bending or flexing, and directs all the force to the pin. It also reduces the tendency for the punch to slip off the pin and scar the barrel.
Get the barrel set up on the block in a FIRM "no-bounce", well braced position.
If needed, have a buddy help hold it.
The idea is, when you tap the sight pins, nothing moves BUT the pin. Otherwise, the force will be dissipated and the pins may upset or deform, locking themselves in tighter.
Use the starter punch to start the pin out. Push from LEFT to RIGHT as you would sight down the barrel.
Look closely at the pins with a magnifier, and you'll often see burrs of metal shaved up off the pins. Push them out from the LEFT side.
Once the pins are moving, switch to the full length punch.
Remove the sight, use lacquer thinner and a tooth brush to clean the slot in the barrel, then dry and apply a coat of rust preventing lube to the slot, the sight, and the pins.
Install the sight and push ONE pin in until it enters the sight hole, then start the other pin (assuming you have a double pin Python.
Install the pins from RIGHT to LEFT.
Then tap the pins in until an equal amount is on each side.