Not possible, today, without involving After Effects to do the text replacement in existing titles.
We plan to enable such programmatic changes within Essential Graphics Template-generated titles, in our next major release.
If you're willing to slum it and use the Legacy Title format then what you want to do is possible via an ExtendScript based panel extension... but there would be hoops to jump through. For example, you can't save a Legacy Title Template with the CC 2017 release, so you'd have to also install an earlier build (eg CC2015) in order to set up your templates.
If that's something you'd want to try then (Legacy) Title Templates (.PRTL) files are XML files that can be easily manipulated programmatically.
Basic process would be to a) read in the Legacy Title Template file and the Excel Spreadsheet, b) for each title instance (from spreadsheet) write a modified copy of the Legacy Title Template file to disk, c) import the generated Title files, d) insert the imported Titles into the sequence accordingly.
I think pretty much everything needed for the above is covered in the various sample panel scripts, especially the PProPanel sample.
The question is, what kind of "titles"?
Are we talking about "open caption type titles", like opening / ending credits or lower thirds, or are we talking about subtitles/closed captions? Both of which could, but the latter definitely should, use timed text, not single burn-in titles.
As long as the challenge is presented in this generic fashion, there's no short answer (even though Bruce has tried ).