Hi @Heather 
Please ask Tofino-related questions in the Intel Forum.
See: Intel(r) Tofino(tm) Family, TNA, and P4Studio questions
As an additional comment, it is different to modify a packet and reply (such as an ARP response or an ICMP response) and use the packet generator (it is probably used in other types of use cases). So be sure to let people know what exactly you want to achieve and they will reply you with the best solution.
Cheers,