Shirishji, What Bhaute explained is the case foryour ghazal. Once you write the opening couplet, the काफिया gets fixed as the HIGHEST COMMON LETTERS. You can not change it afterwards to suit to your NEW shers. What you can do, instead, and this is what I have been trying to convey, is to change the opening sher itself. If you use 'HUNCHHAN/SUTCHHAN' instead of 'HUNCHHAN/BUNCHHAN', all of your shers will be acceptable. Remember, you are FREE to choose whatever काफिया you want to put in the मतला. Choose it wisely. And that would be, use minimum rhyme (minimum COMMON LETTERS at the end), so that you will find tons of हमकाफिया for other shers. हवस त, अब सबैजनाले विश्राम लिम क्यारे, केहि बेर ।