Fine-tuning a template (FM19) to deliver CorpComm's latest idea of styling.
Seems simple and straightforward, doesn't it? but then …
Yep. What you need is Carmen Scripts "Table Cleaner". It cleans the table for old overrides, and makes the styling work again. At least, that might be worth a try IMHO.
I don't quite understand the problem. Is it that tables themselves are not updating when you change the Table Format properties and then click Update? Like Bjorn says, there may be Custom Ruling and Shading overrides on the table that prevent the property from updating. This is sometimes a problem with tables imported from Microsoft Word. Or, your tables may not have true Header rows. Tables from Word don't get true FrameMaker Header rows, so you have to convert the first Body row(s) to Header rows.