Hi,
Text ads are immutable, so you must remove the existing ad and create a new one. This is consistent with the AdWords API, where attempting to modify an existing ad will warn you that you're actually creating a new ad.
A few options you have for frequent updates are:
1. The AdParamService that you mentioned
2. Modify sitelinks or other
feed-based ad extensions. When you change a
FeedItem it updates that item but still retains historical stats.
Cheers,
Josh, AdWords API Team