An experiment is carried out in which the '3-AAUCCC-5' RNA template of TR on the telomerase is mutated.
Will there be a change in the telomeric sequence as a result of this mutation?

Mutation in the RNA template region of the Telomerase would cause adding of mutant DNA sequence at the telomeres.  Yes there will be a change in  the telomeric sequence as a result of this mutation.

Explanation:

Mutation in the RNA template region of the Telomerase would cause adding of mutant DNA sequence.

The enzyme telomerase adds repeated sequence of DNA at the ends of chromosome or telomere.

The mutation could cause shortening of telomeres after each division. It can lead to cell senescence.

The tempelate sequence in the RNA of telomerase directs the synthesis of new DNA in telomeres. The mutation would cause deletion or addition of new nucleotides which will cause defect in telomeric region. The checkpoints will get elicited that will be genetically different.

The telomeres prevent the ends of chromosome from getting stick to the neighboring chromosome.