Here's my .02
-Otto I avoids the British blockade of 1850 and avoids officially entering the Crimean War. Greek uprisings (of OTL) in Albania, Crete, Thessaly, and Macedonia occur and backed in many cases by Greek "volunteers" with covert support from the Empire, especially in Thessaly and Macedonia. With Ottoman attention elsewhere early in the war, the revolts are more successful initially.
-In early November 1853 Ottomans declare war on Greece leading to British and French involvement to protect their investment in Grek debt while bringing the kingdom closer to bankruptcy. With the threat of European involvement against the Ottomans, they come to the bargaining table and negotiate a settlement with Greece following a battle of Sinop.
-Ottomans realize that without European help, the Russians might occupy the Sublime Porte in short order, and as a results Greece keeps Crete, Thessaly, and Macedonia while renouncing claims to Albania and Thrace. Treaty of Thessaloniki (1854) leaves Greece almost doubled in size although the "Magna Grecia" idea takes even stronger root than before
-Otto gains major support and Russian influence remains though is diminished with British favor increased as a result
-Greece prospers and continues to indirectly support irredentalists in parts of the Ottoman territories, Ionian Islands peacefully seceeded by UK on takeover of George I of Greece in 1867 following death of Otto I
-Russo-Turkish War sees Greek involvement with southern FYROM, southern Albania, and many of the Aegean Islands transferred to Greece. Bulgaria becomes a much enlarged state in the resulting Treaty of San Stefano but the revised Treaty of Berlin sees Bulgaria out of Thrace entirely, which Greece sees as ripe for annexation. Greece continues to eye Cyprus but it falls to control of the UK
-Greco-Turkish War of 1897-1898 goes in favor of Greece after rearming with bolt-action rifles and using Crete as a staging ground. With Turkish forces found in western Thrace laying siege to Thessaloniki, Greek marines land by surprise and manage to take Constantinople. International intervention will require them to give it up less than four weeks later with a humiliating peace for the Ottomans, giving Greece control of the rest of (modern FYROM), central Albania, western Thrace, and the western parts of Eastern Rumelia. This brings Bulgarians into conflict with Greece, who see the whole of eastern Rumelia and Thrace as their territory and sets the stage for the Balkan Wars of ten years later.