No rules broken!
I confess to never having used an ATtiny10 but looking at its data sheet it looks to be fairly easy to achieve what you want. I'm not sure what the module with the sim card reader does unless it's just present in the image you copied.
The transmitter and receiver are AM units so there is no real advantage to using Manchester encoding, it shows far more benefit when FM is used because it helps the adaptive data slicer to find the mid point between 0 and 1 in the data stream. In AM systems it is usually more advantageous to add a few mS of 'carrier on' before the data to allow AGC to settle then just send the bits.
The ATtiny10 doesn't have an internal UART so you will have to 'bit bang' the data, I suggest using a timer interrupt to set the speed when transmitting and receiving so they are as close as possible to each other. To receive, look for the first data edge which should be the start bit, wait 1.5 bit intervals then take the next samples at bit rate. Waiting 1.5 bit times should ensure the samples are taken in the middle of the bit periods.
Brian.