Hi Daniel,
Changing the appearance of a text question to multiline will not affect existing data. Early (beta) versions of Survey123 Connect did delete data on all republishing; if you get a warning message about data being deleted, please download the latest version of Survey123 Connect.
I am not changing any changes from text to multiline, am trying to increase the size of a text box, can I do it without affecting my feature service?
Yes, you can do that without affecting the feature service using Survey123 Connect. The particular change you need to do to make the text boxes bigger is to give those questions the appearance multiline.
Thanks, I just need 6 more spaces in this box for email addresses.
Hi. This help topic describes in detail the type of changes in a survey that will force the feature service to be re-created, versus the changes that will not, Publish your survey—Survey123 for ArcGIS | ArcGIS