Not concatenating with plus worked for me:
Find RegExp "tanana"
Replace All "blablabla"
This will keep the old extension of the file. I found a forum post for how to go about stripping the extension here: https://www.ultraedit.com/forums/viewtopic.php?f=10&t=268
(search for Mofi's post Nov 23 2004) But in my case I'm not bothered about it.
If you want to batch edit loads of text files you can use in cmd:
pathto\uedit32.exe pathtodata\*.txt /m,1000="pathtoueditmacro.mac"
where 1000 would be your number of data files; make sure all files in UE are previously closed and all macros deleted from the list; then you could strip the double extension for all files using the bulk rename utility http://www.bulkrenameutility.co.uk/Main_Intro.php