How to trim up voltage on DC-DC converter
What's the likelihood I can use this same formula?


You beat me to the same data sheet I found. More than likely, yes. Manufacturers do not reinvent the wheel unnecessarily, and will use proven designs over and over.

But the TVN 5-2421WI is a dual supply model. And the data sheet has conflicting information if the adjustment can be done, or how it could be done. It says single-output models only in two spots, but also shows a range for the dual output models (±10%). This makes me believe that only one direction of adjustment is available. And since its ±10%, that means only 0.5V or 0.6V. I.E. the positive output can only go up to 5.5V from 5V, and the negative output will match the change equally from -5V to -5.5V. No dropping down below 5V to 4.5V for example.

But since you need ±6V, you likely won't be able to use this for your needs even if the trim works.