Yes, and Yes! Let me explain. . .
In both instances, you need to use the editor.
Open the editor.
Click on 'Scenario'.
Click on 'Custom Rules'.
You should see a bunch of items 'un-gray'.
On the drop down box in the menu bar, click on 'units', and the unit rules screen will open up.
Select the unit you want to give lethal bombardment. In the lower left of the screen is customizable rules.
Now, this bit is very important, so pay attention.
While holding the Ctrl Key, click on Lethal Bombardment Land and/or Lethal Bombardment Sea. Once you've clicked to your hearts content, release the Ctrl key. If you do not hold down the Ctrl key, you will wipe out any other rules that may be active for that unit.
Then, simply save it as 'My Scenario', or whatever.
In Civ3, click on 'Load Scenario', and find 'My Scenario'.
If you want to keep that has a default rule, first go to your Civ3 Directory, and make a backup copy of CIV3.BIC or PTW.BIX (or whatever they call the file. It'll be a .bic file or .bix file for PTW.)
Then copy your 'My Scenario' file to the Civ3/PTW directory, and rename it to the old file name. This will then become the default rules, and your scores will be saved inthe HOF.
It should be noted that if you created a map while doing 'My Scenario', then that'll be your default map. I wouldn't create the Scenario with a map. . ..