addd object style to text

You're absolutely right, Willi. Old habits die hard. Rounded corners can be set as a paragraph-border attribute. So all you need to do, Nick, is define a paragraph style and apply it using a simple Find/Change query.

You'll have to place a text frame in the cells, enable the rounded corners, and place the text in that text frame.

First, create an object style with all the required settings applied (rounded corners, stroke weight, height, and width). Call it 'framed', then use this script.

style = app.documents[0].objectStyles.item ('framed');
app.findGrepPreferences = null;
app.findGrepPreferences.findWhat = '^\\u\\w+$';

// Nothing selected: target document
// Insertion point in cell: target the table
// Otherwise do nothing
if (!app.selection.length) {
  found = app.documents[0].findGrep();
} else if (app.selection[0].parent instanceof Cell) {
  found = app.selection[0].parent.parent.findGrep();
} else {
  exit();
}
  
for (i = found.length-1; i >= 0; i--) {
  f = found[i].insertionPoints[0].textFrames.add();
  f.appliedObjectStyle = style;
  found[i].move (LocationOptions.AT_BEGINNING, f);
}

To text you can only apply Paragraph and Character Styles, never Object Styles. You can automate Character Styles in Paragraph Styles with GREP and Nested Styles and you can include Paragrph Styles in Object and Cell Styles.