One alternative word that can be used instead of "they" is "them."
Another word or phrase that can be used instead of "for this reason" is "therefore" or "as a result".
Substitute or exchange can be used instead of replace.
The term for using one word instead of another but conveying the same meaning is "synonym."
Tone, sound, or expression can be used instead of voice in some contexts.
One alternative word that can be used instead of "they" is "them."
John introduced his comrade, Jason. Comrade isn't used very often nowadays; instead, people just say 'friend'.
instead of being that
no "It" is not used instead of he and she...
used to be
How come is often used instead of why.
But may be used - instead of however, in most contexts.
Silk was introduced to Egypt much later by Romans.
unserrated
herbage
an word that can be used instead of pen
pronoun