"difficult to effect" is a correct and usable phrase in written English.
It means challenging or hard to bring about or achieve. Example: Implementing these new policies will be difficult to effect without the support and cooperation of all employees.
Sometimes a name substitution is undesirable or difficult to effect.
Bureaucratic inertia, EU law and a legacy of old, energy-hungry buildings can make it difficult to effect change.
There was an oversupply of sugar in the hands of wholesale dealers and others in that vicinity at the time, which made it difficult to effect a resale.
What is required, therefore (and what is difficult to effect), is the translation of these impulses of wonder and joy at nature, into ecologically valuable patterns of behaviour.
A legislature or a court, wishing to alter student outcomes, can easily specify a change in a class size, whereas other potential changes are much more difficult to effect.
If the panel is too far removed from what happens inside the company, Professor Sturm said, then it will be difficult to effect lasting changes in its employment and promotion practices, she said.
In determining the effects of depression and antidepressants, it is difficult to distinguish effects of depression from effects of drugs.
Poor recall also made it difficult to detect effect measure modification by drinking and bathing habits.
Therefore, it has been difficult to isolate effects of E2 deficiency from aging effects.
And, in any case, it is difficult to praise effects which have made acting and script so utterly subordinate.
It's not so good at showing more subtle, or difficult to define, effects in subgroups of people.
