How to manipulate the query plan so that I can have more control on memory grants? Let's say I have a complex query and for this query there are huge
Differences between the estimated and actual execution plans.

These differences are causing spillage into tempDb as described here.

The problem is that in this query there are tables that are too big for me to update the statistics.

How can I manipulate the query plan so that I can have more control on memory grants?

I want to avoid memory spillage to tempdb.

In order for this question to be objective and not too broad, we could concentrate for instance on the hash join operator, when can I replace it by a merge join operator?

Are there other operators with memory grant that could be replaced depending on the work load?

Understanding SQL server memory grant

-- Search cache for queries with memory grants:
SELECT t.text, cp.objtype,qp.query_plan
FROM sys.dm_exec_cached_plans AS cp
JOIN sys.dm_exec_query_stats AS qs ON cp.plan_handle = qs.plan_handle
CROSS APPLY sys.dm_exec_query_plan(cp.plan_handle) AS qp
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS t
WHERE qp.query_plan.exist('declare namespace n=''http://schemas.microsoft.com/sqlserver/2004/07/showplan''; //n:MemoryFractions') = 1
I'm not sure I understand how a table is "too big" to update the statistics. When people start calling tables "too big" for anything, they usually start being candidates for table partitioning. In which case you can use incremental statistics to focus your stats updates on the active partitions (the optimizer won't use the per-partition stats independently, but it will still be beneficial for queries and reduces your maintenance because, presumably, not all of your partitions will have significant, or any, data fluctuations between every maintenance window).

Anyway, instead of trying to manipulate which operators are used in order to affect how much memory grant you have (which may make your performance or resource usage worse), why not use hints that control min/max grants directly? KB #3107401 talks about new query hints MIN_GRANT_PERCENT and MAX_GRANT_PERCENT that control the grant a query will get (the article says 2012 SP3, but these were also added in 2014 SP2). 

Tread lightly, though. My suspicion is you are trying to solve the wrong problem with the wrong solution. If the source of the problem is bad estimates, fix that problem.