You can but you have to go into the xml files if you really want to get rid of it,
Step by Step
1) go into MY computer,
2)look for the Civilization file,
3)go to Civ 4 folder,
4)go to BTS folder
5)then go into asset folder,
6)then go to xml,
7)then the technology folder
8)then finally you get an xml file called technology info (there will be two files with similar names, the bigger file is the one you want)
9)Then copy that file and paste it on the desktop, this is the backup in case it goes wrong,
10)Open the file you copied from, You should scroll down to see the names of different techs (like Farming and such)
11) Find the start of the xml line desrcibing Alphapet, then look for ienableespanioge and it should =1, make it = 0 and that turns it off! If you then want espanioge turned on again then make it =1.
ALternatively you could make a mod, (not as hard as it sounds)
1)In the mod folder within the BTS folder, create a folder, name it whatever you want,
2)then within in that new folder, create an "Asset" folder,
3) within that a "XML" folder
4) within in that an "Technology" folder then paste a copy of Technology info files from the directory in the above step by step and change it in the same old way
5) When you next play civ 4 load a mod and the name of your mod should appear and when you play it espanioge should not work!
Hope this helps!

If you want help, feel free to PM me.