One of the cleanest and most flexible way would be using Template Literals.
An advantage of using this is, if you want to display the content of string variable in the text body, it is cleaner and straight forward.
(Please note the usage of backtick characters)
const customMessage = 'This is a test message';
<Text>
{`
Hi~
${customMessage}
`}
</Text>
Would result in
Hi~
This is a test message