Admission to IIIT Guwahati is based on several factors such as the number of available seats, the number of applicants, the category, and the candidate's performance in JEE Main. The cutoff ranks for each program and category may vary from year to year depending on these factors.
However, based on the previous year's cutoff ranks, it seems difficult to get admission to IIIT Guwahati for a CS or ECE program with a CRL rank of 55k in the OBC category. In 2021, the closing rank for CS and ECE programs in the OBC category at IIIT Guwahati was around 28k and 30k respectively.
In any case, you should keep your options open and apply to other colleges as well.
Every year the criteria change in accordance with the cut-off. But I cannot say with certainty that you shall get into it or not. Every time it comes to competition at the time of special round and if you are the lucky one might boundary cut off would be considered.
Yes if you get through, you might get the branch you want to pursue in IIITG but only if you are not from the General category. But, the chance of getting into IIITG is still high for the general category in ECE at least with the rank of 55k as the seats are increased from 80 to 180 in numbers.
Lastly, the increment is only because IIITG is getting a new permanent campus. Though with the rank of 55k, it is hard to get into IIITG but might the factors such as increment in seats and getting a new permanent campus to increase your chances of getting in.