Can we reduce the basic salary of a trainee after completion of his training period so that his CTC remains the same?

Dear Sir, Am Naveen, my question is can we reduce the basic salary of a trainee after completion of his training period so that his CTC remains the same.

Not able to understand your query fully.
As a general practice, companies do pay Stipend to a trainee during his training period. Question of his salary & basic salary does not arise during the period of training.
Of course, now the terminology of Stipend also changed, and now it is termed as 'training allowance'.
As a general practice, basic salary once fixed can not be reduced afterwards. You can change basic salary of a person, by effecting a hike, but not the other way.