Well, as mentioned by Brenden. Make sure you will document the change properly in the project documentation to avoid future issues. Also, I assume you mean the field used in an online form configuration. In this case, the default size is set to 200 characters, you can increase it in \CMS\CMSModules\BizForms\Tools\BizForm_Edit_General.aspx file:
<cms:CMSTextBox ID="txtRedirect" runat="server" MaxLength="200" />
But the hotfix or upgrade may revert it back to defaults.