When you sending out those IR code as RF signal, what receiver would receive them and convert RF back to IR again?
With the Pronto TS1000, it was not intended as an IR extender, but only for X-10 RF. For an IR extender, you could get later Prontos (e.g. TSU3000, TSU9000) that had IR and 418MHz RF (in N. America, 434MHz elsewhere) to send to multiple, addressable RF-to-IR modules made by Philips. The Universal Remote MX3000 also has IR plus 418MHz RF and addressable RF-to-IR modules.
Also, I just discovered that Amazon sells 3-4 310MHz RF remotes for Linear and Stanley garage door openers. They are under $10 but I have no idea whether the RF transmitter section can be easily accessed and repurposed for use in a TS1000.