Displaying the real temperature while sending temperature shift through a setpoint

I am opening a new topic as my problem is no longer linked to my previous post (https://community.openhab.org/t/error-message-translator-couldnt-parse-data-for-datapoint-type-9-001-while-trying-to-configure-a-thermostat-control/74184/2).
I hope this is not a problem.

Ok, I am definitely stupid and a real nuisance !

The remaining problem I have is the following:

I have 4 addresses for the thermostat in a room :

Setpoint shift (1 Byte) : 5 / 0 / 57
Setpoint shift feedback (1 Byte) : 5 / 0 /59
Display temperature (2 Byte) : 5 / 0 / 58
Actual Temperature (2 Byte) : 5 /0 / 54

If I want to change the temperature, the only way I found is through the 5/0/57 (dpt 6.010); this address only accepts +x, 0 or -x where x is (an integer) the difference between the target temperature and the new target temperature I want to reach.
Even if adding or subtracting the “setpoint shift” is working, I would like to display the real target temperature instead of a difference.
I can of course use the js transform and add 21 (which is the present target temperature) but if I change it through the “JUNG Remote” it will no longer be correct.
I tried with a rule but with a rule (and I am perhaps wrong) I can only post something and I do not want to post anything else than the temperature shift;
I do not know if I am “clear” or totally incomprehensible …

My (concerned) things are :

Type number : C_Bureau_Temp_Actuelle "Temperature" [ ga="5/0/54" ]
Type number : C_Bureau_Temp_Cible "Temperature" [ ga="9.001:5/0/58"] 
Type number : C_Bureau_Temp_Shift "Temp Shift" [ga="6.010:5/0/57+<5/0/59"]

Items :

Number Bureau_Temp_Actuelle "Temperature Actuelle [%.1f °C]" {channel="knx:device:bridge:generic:C_Bureau_Temp_Actuelle"}
Number Bureau_Temp_Cible "Temperature Cible [%.1f °C]" {channel="knx:device:bridge:generic:C_Bureau_Temp_Cible"}
Number Bureau_Temp_Shift "Temperature Shift [JS(tempshift2.js):%s]" {channel="knx:device:bridge:generic:C_Bureau_Temp_Shift"}

The tempshift2.js only divides the Bureau_Temp_Shift by 2 as the knx address accepts integer (1 for 0.5 celcius).

My sitemap lines :

Text item=Bureau_Temp_Actuelle icon="temperature"
Text item=Bureau_Temp_Cible icon="temperature"
Setpoint item=Bureau_Temp_Shift minValue=-10 maxValue=10 step=1 icon="temperature"

May I kindly ask you if you would have the “quick fix” to my issue ?

Thanks a lot !!

Have a nice evening.