Is it possible to turn off the automatic fill feature in iMessage.?

Hi digitaldoggy,

There are a few options available you can try to find the solution that works best for you, a few of these are covered at Save keystrokes with text replacements on iPhone.

First, if you open the Settings app on your iPhone and then tap General, followed by Keyboard you'll be able to adjust settings such as Auto-Correction and Predictive text.

If you prefer to keep those features enabled, try this from the article mentioned:

"Have a word or phrase you use and don’t want it corrected?

1. Go to Settings  > General > Keyboard, then tap Text Replacement.
2. Tap  at the top right, then enter your word or phrase in the Phrase field, but leave the Shortcut field blank."

Finally, you can also reset your personal dictionary which seems to have saved your name in all caps:

"Reset your personal dictionary

1. Go to Settings  > General > Reset.
2. Tap Reset Keyboard Dictionary.

All custom words and shortcuts are deleted, and the keyboard dictionary returns to its default state."

Regards.