Ah, should have thought of giving an example

.
But that's not really a big thing, needs only a minor change.
Currently the code looks like this:
PHP:
if (gc.getGame().getGameTurnYear() == gc.getDefineINT("START_YEAR") and not gc.getGame().isOption(GameOptionTypes.GAMEOPTION_ADVANCED_START)):
for iPlayer in range(gc.getMAX_PLAYERS()):
player = gc.getPlayer(iPlayer)
if (player.isAlive() and player.isHuman()):
popupInfo = CyPopupInfo()
popupInfo.setButtonPopupType(ButtonPopupTypes.BUTTONPOPUP_TEXT)
szBody = localText.getText("TXT_KEY_MOD_HEADER", ()) + "\n\n" + localText.getText("TXT_KEY_MOD_TEXT", ())
popupInfo.setText(szBody)
popupInfo.addPopup(iPlayer)
to change the text depending on map, you can just change it in this way:
PHP:
if (gc.getGame().getGameTurnYear() == gc.getDefineINT("START_YEAR") and not gc.getGame().isOption(GameOptionTypes.GAMEOPTION_ADVANCED_START)):
for iPlayer in range(gc.getMAX_PLAYERS()):
player = gc.getPlayer(iPlayer)
if (player.isAlive() and player.isHuman()):
popupInfo = CyPopupInfo()
popupInfo.setButtonPopupType(ButtonPopupTypes.BUTTONPOPUP_TEXT)
szBody = localText.getText("TXT_KEY_MOD_HEADER", ()) + "\n\n" + localText.getText("TXT_KEY_MOD_TEXT", ())
if CyMap().getMapScriptName () =="myMap.CivBeyondSwordWBSave": szBody = localText.getText("TXT_KEY_SOME_OTHER_TEXT_HEADER", ()) + "\n\n" + localText.getText("TXT_KEY_SOME_OTHER_MOD_TEXT", ())
popupInfo.setText(szBody)
popupInfo.addPopup(iPlayer)
if you copy the additional line, then make sure, that if you paste it into your python file, that it has exactly the same number of whitespaces in front of the text like the line above. Do not rely on the whitespaces here, copy them in the file, paste them in the file.
And attention, the map names are case sensitive.