Olga, In your sentence two idiomatic uses of the verb “to be” are combined: the existential [there is/are] which is much like the Russian [есть] and the [be + to be ] construction which can express futurity, pre-arrangement, command, necessity, obligation, etc. And you want to know if you can further complicate this already complex sentence by using an adverb? Yes you can. In fact, the adjective “certain” is already being used adverbially. The [there is/are] construction really has no subject, so there is no available noun, pronoun, or adjective for “certain” to modify. It modifies the verb “are” by default, and so by definition is an adverbial. There are certain to be some changes in the final design. = There are certainly to be some changes in the final design. If “certain” modified the noun “changes”, the meaning would then be “specific changes.” There are to be some certain changes in the final design. All of the adverbs suggested by you and the other Italki members are possible: definitely, probably, likely, unlikely, bound, sure, etc. Any appropriate adverbial that intensified the meaning of the sentence could be used. An adverb like “probably” which weakens the meaning of the sentence is more problematic. Such a sentence would be rare, but still possible. I found one example on the Internet and invented another. Examples: When it comes to network marketing, it’s very important to consider the fact that learning is a never-ending process. It is important that you’re always on top of the game in an ever-changing industry. Not only are there probably to be changes in the niche, but also with the way that you are required to deliver content. Ladies and Gentlemen, You have all worked hard to create an almost flawless prototype. However, I want to inform you ahead of time that since our customer is a perfectionist, there are probably to be some changes in the final design. * When speaking of necessity a more common usage would be "There 'have to' be some changes in the final design.

The wording would be slightly different. There will probably be some changes... [This is different, obviously, from 'certain'] There will definitely be some changes... Also: It is probable that there will be some changes... It is definite that there will be some changes... By the way, I tried to figure out some rule that says why we don't say "There are probable to be..." I can't think of one. We just don't use that combination.

This is obviously someone who thought that "sure" and "certain" are interchangeable in the expression "sure to be:" - There are sure to be some changes in the final design - which is quite correct.

If you wanted to use the exact same sentence structure, you could say "There are likely to be some changes", or "There are bound to be some changes". But for "definitely" and "probably", you will need to change the wording like fdmaxey says.