words = ['text', 'be', 'there']
text = "This is an example [word]. Normally there would [word] something important here but [word] isn't."
print(''.join(w for p in zip(text.split('[word]'), (*words, '')) for w in p))
d29yZHMgPSBbJ3RleHQnLCAnYmUnLCAndGhlcmUnXQp0ZXh0ID0gIlRoaXMgaXMgYW4gZXhhbXBsZSBbd29yZF0uIE5vcm1hbGx5IHRoZXJlIHdvdWxkIFt3b3JkXSBzb21ldGhpbmcgaW1wb3J0YW50IGhlcmUgYnV0IFt3b3JkXSBpc24ndC4iCnByaW50KCcnLmpvaW4odyBmb3IgcCBpbiB6aXAodGV4dC5zcGxpdCgnW3dvcmRdJyksICgqd29yZHMsICcnKSkgZm9yIHcgaW4gcCkp