You have to know the Rich Text Format(RTF) to be able to manually modify the text in an RTF buffer.
An RTF table is defined as a collection of rows that contain cells.
An example;
|---------------------------|
| Row1Cell1 | Row1Cell2 |
|---------------------------|
The corresponding RTF is;
{
\trowd \trgraph180
\cellx1440\cellx2800
\pard\intbl Row1Cell1 \cell
\pard\intbl Row1Cell2 \cell
\trow
}
The curly brackets are optional and added for readability
\trgraph180 - This row has cells with internal margins of at least 180 twips
\cellx1440\cellx2800 - This row contains 2 cells the fist ends at 1440 twips from left margin and the second 2800 twips from left margin.
\pard\intbl Row1Cell1 \cell - Cell contents
\pard\intbl Row1Cell2 \cell - Cell contents