You can also do this without backticks if you put the dot operator at the end of the line. That’s one of the freebie line continuation characters that PowerShell gives you, because it knows that it’s not a complete expression without something to the right of the dot:
$string = 'I am a string'
$string.Replace('string', 'frog').
Replace('am', 'found')
And since you are chaining the replaces, seems like a good opportunity to loop over sets of replacement terms defined in a hash table. It’ll be a lot easier to read and troubleshoot as the number of your replacement terms increases.