Yes done mine. I suggest you dont consider any repair or second hand matrix. The original Diahatsu matrix as factory fitted is brass and it rots at the joints. Any repairs will not last more than a few months and you will then need to do the job again. If you search this site form 'heater matrix' you will find my earlier posts about matrix replacement and a supplier. You can buy a new replacement matrix for about £60 ... diahatsu charge about £300 for matrix plus fitting. The supplier is in Redditch Worces and will mail order ... get their tele number by searching as above.
The task of replacing a matrix is easy but tiresome. Task is easier if you remove both front seats. You need to remove the radio, then raise the whole dashboard, detach the matrix pipes at the engine compartment and then access the heater unit. The most difficult task is finding the fixing screws to undo the dashboard/heater unit - there are visible screws on the side by the doors, screws hidden under the plastic covers on each side of the windscreen, hidden screws behind the dashboard air vents and a hidden screw under the plastic cover holding the dials in the top center of the dashboard. Other screws are obvious but difficult to reach.
If you’re agile you will do the job in about 5 to 6 hours.
NOTE ... be careful not to damage the heater control. The heater switch is easily broken whilst dislodging the heater unit. The switch mechanism is mechanical - it took me some time to repatriate the switch bits!

I recollect a member to this site said he did the job without removing the dashboard .... I dont believe it! You cant access heater unit without releasing the dashboard.