If a resistance is connected in series with the primary of a transformer, what will be the probable effect

Only will cause a voltage drop to the primary voltage.

A resistance, used alone, will reduce the tension from that circuit.

However, in my country, the law says sometjing like this:"it is forbiden to reduce the voltage in a circuit by using a resistance !". Since the resistor will heat it self [P=R*I(^2)] it became a danger - a fire can occur.

Wish you the best! 

Why you  want to add resistance in series with the primary of a transformer? To me it is not advisable.

There is a voltage drop happen in primary voltage (V1) so the secondry transformer voltage (v2) wil be lower than its rate 

eg. if the transformer rate is from24 V to220 V 

24 volt will be say20 Volt after add resistance 

and the secondry will be185 V

if you connect a resistance in series with primary of a transformer it will limit the value of primary current and hence the secondary current will be increased.

Decrease in secondary induced emf.

IF a resistance is connected in series with the primry of transfromer so transfarmer is work but no true

It will decrease the primary current which leads to decrease the secondary current leading to decrease the secondary voltage by other words It will divid the total voltage applied into two voltage one on the series resistance and one on the primary winding and it's values depend on it's resistances any way the winding voltage now is less than the normal .
Transferring smaller value of voltage leads to smaller value in voltage on the secondary winding regardeless it's a step up or down transformer

Two things can happen in connecting a resistance in series with the transformer primary winding. adding a resistor crates voltage drop in it, reducing the primary voltage at the terminals. Hence secondary output will be less. 

Secondly the resistor gets heated up, hence it is not advisable to connect the same to reduce output voltage. Increasing primary resistance increase the inductive reactance, which reduce the magnetizing current, which leads to insufficient core magnetization.

It distorts the sinusoidal voltage of the transformes's sec winding

Decrease in secondary induced emf.