It might be possible, but other problems with the sentence make it difficult to be sure. As soon as I realised . . . has normally to be followed by a main clause containing a verb in the past tense. It cannot be followed by the modal would. The whole sentence really needs recasting. The way you put it depends your relationship with your neighbour, but if the relationship is a formal one, you might want to say something like:
I’m very sorry if the large box outside my room has caused you any
inconvenience over the past three days. I realise it must have made it
difficult for you to get down the corridor, [if appropriate: but
you’ll be pleased to know that I have now removed it.]
Tom is the best expert ...
Assertion of a fact. Where there are agreed criteria then there's no need to hedge an statement.
Djokavic is the current number one male tennis player in the world
When criteria are less certain, or we ourselves are not sure of our facts, or we wish to be modest by appearing to be uncertain of our facts we may use I think
I think Djokavic is the best male tennis played of all time
I think that the population of the UK is 50 million (actually 65 million)
This formulation implies that we are open to correction and discussion
Adding would softens this further, emphasises that we are uncertain
I would think that the population of the UK is greater than 50 million
The I would have thought formulation is normally used in a context where some information has recently been given. Depending upon the context it may imply that we are actually contradicting the information, or that we are expressing surprised acceptance.
I think Tendulakar is the best batsman of all time
I would have thought Bradman had a better record
that was disagreeing, suggesting that by some criteria Bradman is better
The current UK population is 65 million
Oh, I would have thought it was only 50 million
but now I've changed my opinion (this implied but not said)
that was agreeing, I thought it was 50 million, but I accept your statement of 60 million is correct. We could just say
Oh, I thought it was only 50 million
With pretty much the same meaning, the slight difference being that the second case implies it was actively in my mind, whereas the would form could imply that I hadn't really formed a solid opinion until now, but I would probably have guessed 50 million.
As your comment indicates we are indeed into shades of meaning and idioms. In these cases the tone of voice will often differentiate the meaning.
I would have thought Bradman had a better record
Would probably said with a questioning or challenging tone and raised eyebrow.
Best Answer
First let me correct your "weather" to "whether". Then let me say that whether is correct here, and if is not. If addresses one condition that is either true or false; whether addresses two conditions, one of which is true and the other false. Therefore you are correct that if implies a conditional situation and whether does not—the existence of two conditions is unconditional.
That said, the first sentence is not conditional and the second one is; that's the difference. To clarify this, let's rephrase them a bit more formally:
The first sentence says you tried to tell and couldn't, the second says that you expected that if you tried to tell you wouldn't be able to.